The start of the Trisolar Crisis coincided with Cheng Xin's completion of her graduate studies, and she was selected to join the task force working on the design of the propulsion system for the next generation of Long March rockets. To others, this seemed like the perfect job: important and high profile.

But Cheng Xin had lost the enthusiasm for her chosen profession. Gradually, she had come to see chemical rockets as similar to the giant smokestacks of the early Industrial Age. Poets back then had praised those forests of smokestacks, thinking that they were the same as industrial civilization. People now praised rockets the same way, thinking they represented the Space Age. But if humanity relied on chemical rockets, they might never become a true spacefaring race.

The Trisolar Crisis simply highlighted this fact. Trying to build a Solar System defense system based on chemical rockets was pure lunacy. Cheng Xin had made an effort to keep her options open by picking some classes in nuclear propulsion. After the Crisis, all aspects of work within the aerospace system accelerated, and even the long-delayed first-generation space plane project was given the go-ahead. Her task force was also charged with designing the prototype for the engines that would be used by the plane in spaceflight. Professionally, Cheng Xin's future seemed bright: Her abilities were recognized, and in China's aerospace system, most chief engineers began their careers in propulsion design. But since she believed chemical rocketry was yesterday's technology, she didn't think she would get very far in the long term. Heading in the wrong direction was worse than doing nothing at all, but her job demanded her complete focus and attention. She was deeply frustrated.

The PIA Headquarters was located in an old six-story building not far from the UN Headquarters. Dating from the end of the eighteenth century, the building was thick and well-built, like a solid block of granite. When Cheng Xin entered it for the first time after her trans-Pacific flight, she felt a chill, as though entering a castle. The place wasn't at all what she had expected from an intelligence agency for the whole world; it reminded her more of a place where byzantine plots were hatched through whispers.

Cheng Xin took the job without hesitation.

Then came an opportunity for her to leave chemical rockets behind. The United Nations began to create all sorts of agencies related to planetary defense. Unlike UN agencies from the past, these new agencies reported directly to the PDC, and were staffed by experts from various nations. The Chinese aerospace system sent many people to these agencies. A high-level official offered Cheng Xin a new position: Aide to the director of the Technology Planning Center for the PDC Strategic Intelligence Agency. Humanity's intelligence-gathering work against the Trisolarans had so far focused on the ETO, but the PDC Strategic Intelligence Agency, or PIA, would focus their efforts directly on the Trisolaran Fleet and the home world of Trisolaris itself. They needed people with strong backgrounds in the technical aspects of aerospace technology.

The building was mostly empty; she was among the first to report for duty. In an office full of unassembled furniture and just-unsealed cardboard boxes, she met her boss, PIA's Technology Planning Center director.

Mikhail Vadimov was in his forties, muscular, tall, and spoke English with a heavy Russian accent. It took a few moments before Cheng Xin even realized that he was speaking English. He sat on a cardboard box and complained to her that he had worked in the aerospace industry for more than a dozen years and had no need for any technical assistance. Every country was eager to fill the PIA with its own people, but much less willing to give cold, hard cash. Then he seemed to realize that he was talking to a hopeful young woman who was growing rather dejected from his speech, and tried to comfort her by saying: "If this agency manages to make history -- a big possibility, even if it probably won't be very good history -- we two will be remembered as the first to show up!"

Cheng Xin was cheered by the fact that she and her boss had both worked in aerospace. She asked Vadimov what he had worked on. He carelessly mentioned a stint on the Buran spacecraft; then that he'd served as the executive chief designer for a certain cargo-carrying spaceship; but after that, his explanations turned vague. He claimed that he had done a couple of years in diplomacy, then entered "some department" that "did the same kinds of things we do now."

"The chief is here also. His office is upstairs. You should swing by and say hi, but don't take up too much of his time."

"It's best if you don't probe too much into the employment histories of your future colleagues, okay?" Vadimov said.

As soon as Cheng Xin walked into the PIA chief's spacious office, she was greeted by the strong smell of cigar smoke. A large painting hung on the wall. A leaden sky and the dim, snow-covered ground took up most of the painting; in the distance, where the clouds met the snow, a few dark shapes lurked. A closer examination revealed them to be dirty buildings, most of them one-story clapboard houses mixed with a few European-style houses with two or three stories. Based on the shape of the river in the foreground and other hints in the geography, this was a portrait of New York at the beginning of the eighteenth century. The overwhelming impression given off by the painting was coldness, which Cheng Xin thought fit the person sitting under the painting rather well.

Next to the large painting was a smaller picture. The main subject in the painting was an ancient sword with a golden cross guard and a bright, shining blade, held in a hand enclosed in bronze gauntlets -- only the forearm was shown. The hand was lifting the sword to pick up a wreath woven from red, white, and yellow flowers floating over the water. In contrast to the larger painting, this picture was bright and colorful, but it nonetheless radiated eeriness. Cheng Xin noticed that bloodstains covered the white flowers in the wreath.

PIA Chief Thomas Wade, an American, was far younger than Cheng Xin had expected -- he looked younger than Vadimov. He was also more handsome, with very classical features. Later, she would conclude that the classical appearance came mostly from Wade's expressionless face, like a cold, lifeless statue transplanted out of the cold painting behind him. Wade didn't look busy -- the desk in front of him was completely empty, with no sign of a computer or paper documents. He glanced up as she entered, but returned to contemplating the cigar in his hand almost right away.

Cheng Xin thought she saw exhaustion and laziness in those eyes, but there was also something deeper, something sharp that made her uncomfortable. A smile appeared on Wade's face, like water seeping out of a crack in the frozen surface of a river; there was no real warmth, and it didn't relax her.

Cheng Xin introduced herself and expressed her pleasure at having a chance to study from him, and continued until Wade lifted his eyes to look at her.

She tried to respond with a smile of her own, but the first words out of Wade's mouth froze her face and entire body. "Would you sell your mother to a whorehouse?"

After she told Vadimov what had happened, Vadimov laughed. "That's just a line that used to be popular in our… trade. I heard it started back during the Second World War. Veterans would use it as a joke on novices. The point is: Our profession is the only one on Earth where lies and betrayal are at the very heart of what we do. We have to be… flexible when it comes to commonly accepted ethical norms. PIA is formed from two groups of people: Some are technical experts like you; others are veterans of the various intelligence agencies in the world. These two groups have different ways of thinking and acting. It's a good thing that I'm familiar with both and can help you adjust to the other."

Cheng Xin shook her head no, but she wasn't even trying to respond to the question; she was terrified that she had not understood what he said. But Wade waved at her with his cigar. "Thanks. Go do what needs to get done."

Two days after Cheng Xin's arrival, PIA held its first all-hands meeting, even though not everyone had shown up yet. Other than PIA Chief Wade, there were three assistant chiefs: one from China, one from France, and one from the United Kingdom.

They were polite to each other, but there was no trust. The technical experts kept to themselves and acted as if they were on guard against theft every minute. The intelligence veterans were gregarious and friendly -- but they were constantly on the lookout for something to steal.

"But our enemy is Trisolaris. This is nothing like traditional intelligence."

Over the next few days, other new PIA staff members reported for duty. Most of them came from countries that were permanent members of the PDC.

Assistant Chief Yu Weiming spoke first. Cheng Xin had no idea what kind of work he had done in China -- and he had the sort of face that took multiple meetings to remember what he looked like. Fortunately, he didn't engage in the habit -- common among Chinese bureaucrats -- of giving long, meandering speeches. Though he was just repeating platitudes about the PIA's mission, at least he spoke succinctly.

It was just like Vadimov had predicted: These people were far more interested in spying on each other than gathering intelligence on Trisolaris.

"Some things are constant."

While Assistant Chief Yu was giving this speech, Cheng Xin noticed that Wade was kicking the table legs and slowly maneuvering his chair away from the conference table as though he didn't want to be there. Later, whenever anyone asked him to say a few words, he shook his head and refused.

Finally, after everyone who wanted to make a speech had done so, he spoke. Pointing at the pile of boxes and fresh office supplies in the meeting room, he said, "I'd like the rest of you to take care of these matters on your own." Apparently, he was referring to the administrative details of getting the agency up and running. "Please don't take up my time or theirs"-- here he pointed at Vadimov and his staff. "I need everyone in the Technology Planning Center with experience in spaceflight engineering to stay. The rest of you are dismissed."

Assistant Chief Yu said that he understood that everyone in the PIA was sent by their own country, and so they had dual loyalties. PIA didn't demand, and didn't even hope, that they would place their loyalty to the agency above their duties to their own nations. However, since the PIA's task was the protection of the entire human race, he hoped that everyone present would at least try to balance the two appropriately. Considering that the PIA was going to work directly against the Trisolaran threat, they ought to become the most united of the new agencies.

"What are the specific requirements?" asked Vadimov. He was the only one who seemed to take Wade's announcement in stride.

About a dozen people remained in the now much less crowded conference room. As soon as the heavy oak doors closed, Wade dropped his bomb. "The PIA must launch a spy probe at the Trisolaran Fleet."

The stunned staff members looked at each other. Cheng Xin was surprised as well. She had certainly hoped to get to substantive technical work quickly, but she hadn't expected such directness or speed. Considering that the PIA had just been formed and there were, as yet, no national or regional branches, it seemed ill-equipped to take on big projects. But the real shocker was the boldness of Wade's proposal: The technical challenges and other barriers seemed insurmountable.

"I've consulted with the delegates of the permanent members of the PDC in private, but the idea hasn't yet been formally presented. Based on what I know, the PDC members are most interested in one specific requirement -- and this is something that they won't compromise on: The probe must achieve one percent of lightspeed. The permanent members of the PDC have different ideas about other parameters, but I'm sure they'll come to some compromise during formal discussions."

Wade shook his head. "With those sophons zipping about at lightspeed, spying on us constantly, and completely blocking all fundamental physics research, it's no longer certain that we'll make significant technological progress in the future. If humanity is doomed to crawl at a snail's pace through space, we'd better get started as soon as possible."

Cheng Xin suspected that Wade's plan was at least partly motivated by politics. The first effort by humanity to make active contact with an extraterrestrial civilization would enhance the PIA's status.

An expert from NASA spoke up. "Let me get this straight. Given those mission parameters, and supposing we only worry about acceleration and provide no way for the probe to decelerate, the probe will take two to three centuries to reach the Oort Cloud. There, it will intercept and examine the decelerating Trisolaran Fleet. Forgive me, but this seems a project better reserved for the future."

"But given the current state of spaceflight technology, it will take twenty, maybe thirty thousand years to reach the Oort Cloud. Even if we launch the probe right now, we won't have gotten very far from Earth's front door by the time the Trisolaran Fleet arrives in four hundred years."

"That is precisely why the probe must achieve one percent of lightspeed."

Wade slammed his fist down on the table. "You forget that we now have resources! Before, spaceflight was merely a luxury, but now it's an absolute necessity. We can ask for resources that far exceed what was imaginable before. We can throw resources at this problem until the laws of physics bend. Rely on brute force if you have to, but we must accelerate the probe to one percent of lightspeed!"

"You're talking about boosting our current maximum speed a hundredfold! That requires a brand-new form of propulsion. We can't achieve that kind of acceleration with current technology, and there's no reason to expect a technical breakthrough within the foreseeable future. This proposal is fundamentally impossible."

Vadimov instinctively looked around the room. Wade glanced at him. "Don't worry. There are no reporters or outsiders anywhere near here."

Vadimov laughed. "Please don't take offense. But saying we want to throw resources at the problem until the laws of physics bend is going to make our agency the laughingstock of the world. Please don't repeat it in front of the PDC."

Everyone held their tongue. The staff just wanted the meeting to be over. Wade looked at everyone in turn, then returned his gaze to Cheng Xin. "No, not everyone. She's not laughing." He pointed at her. "Cheng, what do you think?"

Cheng Xin was even more baffled. MD? McDonald's? Doctor of medicine?

"But you're Chinese! How can you not know MD?"

Under Wade's keen gaze, Cheng Xin felt as if he were pointing a sword at her, not a finger. She looked around helplessly. Who was she to talk?

Cheng Xin looked at the other five Chinese in the room; they looked just as confused.

"We need to implement MD here," said Wade.

"During the Korean War, the Americans discovered that even common Chinese soldiers taken as prisoners seemed to know a lot about their own field strategies. It turned out that your commanders had presented the battle plans to the troops for mass discussion, hoping thereby to find ways to improve them. Of course, if you become Trisolaran prisoners of war in the future, we don't want you to know that much."

"I already know you're all laughing at me."

Cheng Xin began: "I do have an idea --"

A few of those present laughed. Cheng Xin finally understood that MD meant "military democracy." The others in the conference room enthusiastically supported Wade's proposal. Of course, these elite experts didn't expect a mere technical aide to have any brilliant ideas, but they were mostly men, and they thought that by giving her a chance to talk, they would have a perfect excuse to appreciate her physical attributes. Cheng Xin had always made an effort to dress conservatively, but this sort of harassment was something she had to deal with constantly.

"Well, more like getting around the laws of physics." Cheng Xin smiled at Camille politely. "The most promising resource at our disposal is the stockpile of nuclear weapons from around the world. Without some technical breakthrough, these represent the most powerful sources of energy we can launch into space. Imagine a spaceship or probe equipped with a radiation sail, similar to a solar sail: a thin film capable of being propelled by radiation. If we set off nuclear bombs behind the sail periodically --"

"An idea for bending the laws of physics?" The speaker was an older Frenchwoman named Camille, a highly respected and experienced consultant from the European Space Agency. She looked at Cheng Xin contemptuously, as though she didn't belong in the room.

"She didn't manage to bend the laws of physics, but she did fulfill the other aspect of the chief's demand," another consulting expert said. "I'm just sorry to see such a pretty girl fall under the spell of brute force." The wave of laughter reached a crescendo.

A few titters. Camille laughed the loudest. "My dear, you have sketched for us a scene out of a cartoon. Your spaceship is filled with a pile of nuclear bombs, and there's a giant sail. On the ship is a hero who bears more than a passing resemblance to Arnold Schwarzenegger. He tosses the bombs behind the ship, where they explode to push the ship forward. Oh, it's so cool!" As the rest of the staff joined in the mirth, she continued. "You may want to review your homework from freshman year in college and tell me: one, how many nuclear bombs your ship will have to carry; and, two, with that kind of thrust-to-weight ratio, what sort of acceleration you can achieve."

"The bombs will not be on the ship," Cheng Xin replied calmly. The laughter ceased abruptly; it was as if she had put her hand on the surface of a struck cymbal. "The probe itself will be a tiny core equipped with sensors attached to a large sail, but the total mass will be light as a feather. It will be easy to propel it with the radiation from extravehicular nuclear detonations."

The conference room became very quiet. Everyone was trying to think where the bombs would be. While the others were mocking Cheng Xin, Wade's mien had remained chilly and unmoved. But now, that smile, like water seeping from a crack in the ice, gradually reappeared on his face.

Cheng Xin retrieved a stack of paper cups from the drinking water dispenser behind her and laid them out on the conference table in a line. "We can use traditional chemical rockets to launch the nuclear bombs in advance, and distribute them along the first segment of the probe's route." She took a pencil and moved its tip along the line, from one cup to the next. "As the probe passes each bomb, we detonate it right behind the sail, accelerating it faster and faster."

The men now moved their gazes away from Cheng Xin's body. They were finally willing to take her proposal seriously. Only Camille continued to stare at her, as though at a stranger.

"We can call this technique 'en-route propulsion.' This initial segment is the acceleration leg, and it takes up only a tiny fraction of the overall course. As a very rough estimate, if we use one thousand nuclear bombs, they can be distributed along a path of about five astronomical units stretching from the Earth to Jupiter's orbit. Or we could even compress it further and distribute the bombs within Mars's orbit. That's definitely achievable with our current technology."

The silence was broken by a few whispers. Gradually, the voices grew louder and more excited, like a drizzle turning into a rainstorm.

Cheng Xin smiled at him. "It's based on an old idea in aerospace circles. Stanislaw Ulam first proposed something like it back in 1946. It's called nuclear pulse propulsion."

"You didn't just come up with this idea, did you?" asked Wade. He had been listening to the discussion intently.

"Dr. Cheng," Camille said, "we all know about nuclear pulse propulsion. But those previous proposals all required the fuel to be carried aboard the ship. The idea of distributing the fuel along the spacecraft's route is indeed your invention. At least, I've never heard the suggestion before."

Wade slammed the table again. "Enough! Don't get bogged down on details right now. We're not evaluating feasibility; rather, we're trying to figure out if it's worthwhile to study the idea's feasibility. Focus on big-picture barriers."

The discussion grew heated. The assembled experts tore into the idea like a pack of hungry wolves presented with a piece of fresh meat.

After a brief silence, Vadimov said, "The best thing about this proposal is that it's easy to get started."

A few seemed to want to speak up, but finally decided to remain quiet. None of them thought their own ideas could compete with Cheng Xin's. Eventually, everyone's eyes focused on her again, but this time, the meaning was completely different.

Everyone immediately caught on to Vadimov's meaning. The first step in Cheng Xin's plan involved launching a large number of nuclear bombs into orbit around the Earth. Not only did humanity possess such technology, the bombs were already on launch vehicles: the ICBMs in service could easily be repurposed for this use. American Peacekeepers, Russian Topols, and Chinese Dongfengs could all directly launch their payloads into near-Earth orbits. Even intermediate-range ballistic missiles, if retrofitted with booster rockets, could do the job. Compared to the post-Crisis nuclear disarmament plans that required destroying the missiles, this plan would be far cheaper.

"Excellent. For now, let's pause our discussion of Cheng Xin's en-route propulsion idea. Any other proposals?" Wade looked around the room.

"Since the probe's velocity would go up a level each time a bomb explodes, it's a bit like climbing a flight of stairs," Vadimov said. "I suggest we call it the Staircase Program. Besides the requirement of a final velocity exceeding one percent of lightspeed, another parameter to keep in mind is the mass of the probe."

"We'll meet twice more to brainstorm and see if we can come up with a few more options. But we might as well get started on the feasibility study for en-route propulsion. We'll need a code name."

"Then the key will be the mass of the probe itself."

"A radiation sail can be made very thin and light. Based on the current state of material sciences, we can make a sail of about fifty square kilometers and limit the mass to about fifty kilograms. That should be big enough." The speaker was a Russian expert who had once directed a failed solar sail experiment.

"If we include some basic sensors and take into account the necessary antenna and radioisotope power source to transmit information back from the Oort Cloud, about two to three thousand kilograms ought to do it."

Everyone's eyes turned to another man in the room, the chief designer of the Cassini-Huygens probe.

"No!" Vadimov shook his head. "It has to be like Cheng Xin said: light as a feather."

"If we stick with the most basic sensors, maybe one thousand kilograms would be enough. I can't guarantee that's going to succeed -- you're giving me almost nothing to work with."

"You're going to have to make it work," said Wade. "Including the sail, the entire probe cannot exceed one metric ton in mass. We'll devote the strength of the entire human race to propel one thousand kilograms. Let's hope that's light enough."

During the next week, Cheng Xin slept only on airplanes. As part of a task force led by Vadimov, she shuttled back and forth between the space agencies of the US, China, Russia, and Europe to coordinate the feasibility study of the Staircase Program. During that week, Cheng Xin got to travel to more places than she had in her life up to that point, but she didn't get to do any sightseeing except through the windows of cars and conference rooms.

At first, they had thought they could get all the space agencies to do a combined feasibility study, but that turned out to be an impossible political exercise. In the end, each space agency performed an independent analysis. The advantage of this approach was that the four studies could be compared to get a more accurate result, but it also meant that the PIA had to do a lot more work. Cheng Xin worked harder on this project than anything in her professional career -- it was her baby, after all.

Wade's expression didn't change. "Don't be sad. I have even worse news: At the last session of the PDC, the resolution proposing the Staircase Program was voted down."

Then came some very bad news: In order to reach the required speed of 1 percent of lightspeed, the mass for the entire probe assembly had to be reduced by 80 percent -- to only 200 kilograms. Subtracting the mass reserved for the sail left only 180 kilograms for sensors and communication devices.

Of the seven permanent members of the PDC, four voted no. Their reasons were surprisingly similar. In contrast to the technical staff of the PIA with background in spaceflight, the delegates were not interested in the propulsion technology. They objected that the probe's intelligence value was too limited -- in the words of the American representative, "practically nil."

The four feasibility studies quickly reached preliminary conclusions, which were very similar to each other. The good news was that the area of the radiation sail could be shrunk to twenty-five square kilometers, and with even more advanced materials, the mass of the sail could be reduced to twenty kilograms.

Moreover, due to the presence of sophons, the plan for sending a probe would be completely transparent to the enemy, making its chances of successfully gathering any valuable intelligence nonexistent. Considering the enormous investment required to implement such a plan, the benefits were too minuscule. Most of the plan's value was purely symbolic, and the great powers were simply insufficiently interested. The other three permanent members of the PDC voted yes only because they were interested in the propulsion technology.

This was because the proposed probe had no way to decelerate. Even taking into account the fact that the Trisolaran Fleet would be decelerating, the probe and the fleet would pass by each other at a relative speed of around 5 percent of lightspeed (assuming the probe wasn't captured by the fleet). The window for gathering intelligence would be extremely small. Since the small mass of the probe made active sensors such as radar impractical, the probe was limited to passive sensing, mainly of electromagnetic signals. Given the advanced state of Trisolaran technology, it was almost certain that the enemy would not be using electromagnetic radiation, but media such as neutrinos or gravitational waves -- techniques beyond the current state of human technology.

"And the PDC is right," said Wade.

"What's our next step?" asked Vadimov.

Everyone silently mourned the Staircase Program. Cheng Xin was the most disappointed, but she comforted herself that as a young person with no record of achievements, having gotten this far on her first original idea wasn't too bad. Certainly, she had exceeded her own expectations.

"Ms. Cheng, you look unhappy," Wade said. "Apparently you think we're going to back off from the Staircase Program."

"We're not going to stop." Wade stood up and paced around the conference room. "From now on, whether it's the Staircase Program or any other plan, you do not stop until I tell you to stop. Understand?" He dropped his habitual indifferent tone and screamed like a crazed wild animal. "We're going to advance! Advance! We'll stop at nothing to advance!"

Everyone now stared at Wade, speechless.

Wade was standing right behind Cheng Xin. She felt as if a volcano had erupted behind her, and she cringed and almost screamed herself.

"We're going to send a person."

Wade kicked the leg of the conference table and sent his chair flying backwards so that he could sit behind everyone as they continued to discuss. But no one spoke. It was a repeat of the meeting a week ago when he had first brought up the idea of sending a probe to the Trisolaran Fleet. Everyone tried to chew over his words and unravel the riddle. Shortly, they came to see that the idea wasn't as ridiculous as it seemed at first.

Wade had resumed his calm, emotionless voice. Still in shock at his explosion, it took a while before those in the room understood what Wade meant. He wasn't talking about sending someone to the PDC, but out of the Solar System. He was proposing sending a live scout to the bleak, frigid Oort Cloud one light-year away to spy on the Trisolaran Fleet.

Hibernation was a relatively mature technology. A person could complete the voyage in suspended animation. Assuming the person weighed 70 kilograms, that left 110 kilograms for the hibernation equipment and the hull -- which would resemble a coffin. But what then? Two centuries later, when the probe met the Trisolaran Fleet, how would they wake this person up, and what could he or she do?

"This would require the Trisolaran Fleet to capture the probe," Vadimov said. "And to keep our spy."

"This is very likely." Wade looked up. "Isn't it?" Those inside the conference understood that he was speaking to the sophons hovering around them like ghosts. Four light-years away, on that distant world, other invisible beings were also "attending" their meeting. The presence of the sophons was something that people tended to forget. When they remembered it, besides fright, they also felt a kind of insignificance, as though they were a swarm of ants under the magnifying glass of some playful, cruel child. It was very difficult to maintain confidence when one realized that whatever plans one came up with would be known by the enemy long before they were even explained to the supervisor. Humanity had to struggle to adjust to this kind of warfare, in which they were completely transparent to the enemy.

These thoughts revolved inside the heads of everyone present, but no one spoke up. But Wade seemed to be reading everyone's minds."We need to send a representative of humanity into the heart of the enemy," he said.

In traditional intelligence warfare, sending a spy whose identity was known to the enemy was a meaningless gesture. But this war was different. Sending a representative of humanity into the Trisolaran Fleet was, by itself, a valiant gesture, and it made no difference that the Trisolarans would know the individual's identity ahead of time. The PIA didn't even need to figure out what the spy had to do once he or she got there: As long as the person could be safely and successfully inserted into the fleet, the possibilities were endless. Given that the Trisolarans were transparent in thought and vulnerable to stratagems, Wade's idea became even more attractive.

But now, Wade seemed to have changed the situation slightly. In his scenario, the enemy's knowledge of the plan was an advantage. The Trisolarans would know every detail about the trajectory of the probe, and could easily intercept it. Even though the sophons allowed the Trisolarans to learn about humanity, surely they would still be interested in capturing a live specimen for up-close study.

We need to send a representative of humanity into the heart of the enemy.

A new technology can transform society, but when the technology is in its infancy, very few people can see its full potential. For example, when the computer was first invented, it was merely a tool for increasing efficiency, and some thought five computers would be enough for the entire world. Artificial hibernation was the same. Before it was a reality, people just thought it would provide an opportunity for patients with terminal illnesses to seek a cure in the future. If they thought further, it would appear to be useful for interstellar voyages. But as soon as it became real, if one examined it through the lens of sociology, one could see that it would completely change the face of human civilization.

All this was based on a single idea: Tomorrow will be better.

Excerpt from A Past Outside of Time. Hibernation: Man Walks for the First Time Through Time

This was a relatively new faith, a product of the last few centuries before the Crisis. Previously, such an idea of progress would have been laughable. Medieval Europe was materially impoverished compared to the Classical Rome of a thousand years earlier, and was more intellectually repressed. In China, the lives of the people were worse during the Wei, Jin, and Southern and Northern Dynasties compared to the earlier Han Dynasty, and the Yuan and Ming Dynasties were much worse than the earlier Tang and Song Dynasties. But after the Industrial Revolution, progress became a constant feature of society, and humanity's faith in the future grew stronger.

When examined from the perspective of sociology, the biotechnology breakthrough of human cloning was far less complicated than hibernation. Cloning raised moral questions, but they mostly troubled those with a moral view influenced by Christianity. The troubles brought about by hibernation, on the other hand, were practical, and affected the entire human race. Once the technology was successfully commercialized, those who could afford it would use it to skip to paradise, while the rest of humanity would have to stay behind in the comparatively depressing present to construct that paradise for them. But even more worrisome was the greatest lure provided by the future: the end of death.

If hibernation were possible, why would you linger in the present?

This faith reached its apex on the eve of the Trisolar Crisis. The Cold War had been over for some time, and though problems such as environmental degradation persisted, they were merely unpleasant. The material comforts of life improved at a rapid pace, and the trend seemed to accelerate. If one surveyed people about visions of the future, they might give different answers for how things would be in ten years, but few would doubt that in another hundred years, humanity would be living in paradise. It was easy to believe such a thing: They could just compare their own lives with the lives of their ancestors a hundred years earlier!

But the Trisolar Crisis changed everything. In a single night, the paradise of the future turned into a hell on Earth. Even for terminal patients, the future no longer appealed: By the time they woke up, perhaps the world would be bathed in a sea of fire, and they wouldn't even be able to find an aspirin.

The situation was akin to the dire conditions of post-Crisis Escapism. Later, historians would call it Early Escapism or Time Escapism. Thus, even pre-Crisis, governments around the world suppressed hibernation technology more zealously than cloning technology.

Thus, after the Crisis, hibernation was allowed to develop without constraints. Soon, the technology became commercially viable, and the human race possessed the first tool that allowed them to traverse large swaths of time.

As modern biology advanced apace, people began to believe that death's end would be achievable in one or two more centuries. If so, those who chose hibernation were taking the first steps on the staircase to life everlasting. For the first time in history, Death itself was no longer fair. The consequences were unimaginable.

Cheng Xin went to Sanya on Hainan Island to research hibernation.

This tropical island seemed an incongruous site for the largest hibernation research center, which was operated by the Chinese Academy of Medical Sciences. While it was the middle of winter on the mainland, spring ruled here.

The hibernation center was a white building hidden behind lush vegetation. About a dozen test subjects inside engaged in experimental, short-term hibernation. So far, no one had been put into hibernation with the intent of crossing the centuries.

Cheng Xin first asked whether it was possible to shrink the equipment necessary to support hibernation down to one hundred kilograms. The director of the research center laughed. "One hundred kilograms? You'd be lucky getting it down to one hundred metric tons!"

Crisis Era, Years 1-4, Cheng Xin

The director was exaggerating, but only slightly. He showed Cheng Xin around the center, and Cheng Xin learned that artificial hibernation didn't exactly match its public image. For one thing, it didn't involve ultra-low temperatures. The procedure replaced the blood in the body with an antifreeze cryoprotectant, then brought the body temperature down to minus-fifty-degrees Celsius. Relying on an external cardiopulmonary bypass system, the body's organs maintained an extremely low level of biological activity. "It's like standby mode on a computer," said the director. The entire system -- hibernation tank, life-support system, cooling equipment -- weighed about three metric tons.

"What are you all looking at? I'm not God!" Wade surveyed the conference room. "Why do you think your countries sent you here? To collect a paycheck and to give me bad news? I don't have a solution. Finding a solution is your job!" He kicked the leg of the conference table, and his chair slid back farther than ever. Ignoring the conference room's non-smoking rule, he lit up a cigar.

As Cheng Xin discussed possible ways to miniaturize the hibernation setup with the center's technical staff, she was startled by a realization: If the body's temperature must be maintained around minus-fifty-degrees Celsius, then in the frigid conditions of outer space, the hibernation chamber needed to be heated, not cooled. In the long journey through trans-Neptunian space in particular, outside temperature would be close to absolute zero. In contrast, minus-fifty-degrees Celsius was like the inside of a furnace. Considering that the journey would take one to two centuries, the most practicable solution was radioisotope heating. The director's claim of one hundred metric tons was thus not too far from the truth.

Cheng Xin returned to PIA Headquarters and gave her report. After synthesizing all relevant research results, the staff again sank into depression. But this time, they gazed at Wade with hope.

The rest of the team looked at her, looked at each other, and then turned to the hibernation experts. They shook their heads, uncertain what Cheng Xin meant.

"Maybe…" Cheng Xin looked around hesitantly. She was still unused to MD.

The attendees turned their attention back to the new hibernation experts in the room. None of them said anything, but they made no effort to disguise the anger and frustration of professionals faced with ignorant zealots who were asking for the impossible.

"Maybe… we don't need to send a live person."

"Advance! We stop at nothing to advance!" Wade spewed smoke at her along with the words.

"We could flash-freeze a person to minus-two-hundred-degrees Celsius or below, then launch the body. We wouldn't need life support or heating systems, and the capsule holding the body could be made very small and light. The total mass should not exceed one hundred and ten kilograms. For us, such a body is a corpse, but that may not be the case for Trisolarans."

"Very good," Wade said, and nodded at her. This was the first time he had praised one of his staff since she had known him.

One of the hibernation experts said, "You're talking about cryopreservation, not hibernation. The biggest barrier to reanimating a flash-frozen body is preventing cell damage from ice crystals during the thawing process. It's like what happens to frozen tofu: When you defrost it, it turns into a sponge. Oh, I guess most of you haven't had frozen tofu." The expert, who was Chinese, smiled at the confused Western faces around him. "Now, maybe the Trisolarans know techniques to prevent such damage. Perhaps they can restore the body to normal temperature within an extremely short period of time: a millisecond, or even a microsecond. We don't know how to do such a thing, at least not without vaporizing the body in the process."

Cheng Xin wasn't paying much attention to this discussion. Instead, she was focused on one thing: Who would this minus-two-hundred-degree corpsicle that would be shot into deep space be? She was trying her hardest to advance without regard for consequences, but she couldn't help but shudder at the thought.

Since the special session of the General Assembly was going to announce the Wallfacer Project to the world tonight, the PDC session was delayed by more than an hour. PIA personnel waited in the lobby outside the General Assembly Hall. During previous PDC sessions, only Wade and Vadimov were allowed to attend, while others had to remain outside, waiting to be summoned if their specific area of technical expertise was needed. But this time, Wade asked Cheng Xin to accompany him and Vadimov to the PDC session itself, a high honor for a lowly technical aide.

The latest version of the Staircase Program was brought back to the current PDC session for a vote. Private discussions between Wade and the delegates of the various nations called for optimism. Since the plan, as modified, would represent the first direct contact between humanity and an extraterrestrial civilization, its meaning was qualitatively different from merely sending a probe. Moreover, the person sent to the Trisolarans could be said to represent a ticking bomb implanted in the heart of the enemy. By skillfully using humanity's absolute superiority in tricks and ruses, he or she could change the course of the entire war.

"Who are the Wallfacers?" asked Wade. His tone indicated no particular interest.

After the General Assembly finished its announcement, Cheng Xin and the others watched as a man surrounded by a swarm of reporters passed through the lobby and left the building through another exit -- clearly one of the just-revealed Wallfacers. Since everyone from the PIA was focused on the Staircase Program, most weren't interested in the Wallfacers, and only a couple of them left the building to catch a glimpse of the man. Thus, when the famous assassination attempt of Luo Ji occurred, no one from the PIA heard the gunshot; they only saw the sudden commotion through the glass doors. Cheng Xin and the others ran outside and were immediately blinded by the bright searchlights from helicopters hovering overhead.

"Oh my God, one of the Wallfacers has been killed!" One of her colleagues ran over. "I heard that he was shot several times. In the head!"

"I'm not too sure either. I think three of them are from the pool of well-known candidates. But this fourth one, the one who was shot, was one of your people." He pointed at Cheng Xin. "But no one had heard of him. He's just some guy."

"In this extraordinary time, no one is 'just some guy,'" Wade said. "Any random person could suddenly be handed a heavy responsibility, and anyone important could be replaced at any time." He looked at Cheng Xin and Mikhail Vadimov in turn. Then a PDC secretary called him aside.

Vadimov held up his hand to stop her. The bright searchlight from one of the helicopters shone through his palm and revealed the blood under his skin. "He wasn't joking. Our agency does not need to follow normal HR procedures. You're steady, calm, hardworking, and also creative; you display a sense of responsibility far above your official position. This is a rare combination of qualities in someone your age. Xin, really, I'm glad that you could replace me -- but you can't do quite what I can do." He looked around at the chaos surrounding them. "You won't sell your mother to a whorehouse. You're still a child, when it comes to that aspect of our profession. My fervent hope is that you will always remain so."

"Mikhail, I --"

"He's threatening me," Vadimov whispered to Cheng Xin. "He threw a fit yesterday and told me that you could easily replace me."

"Fuck them all!" Camille screamed. Even with the helicopters thundering overhead, a few onlookers turned to stare. "Fucking pigs don't know how to do anything except fuck around down here in the mud."

"Who are you talking about?" asked Vadimov.

"Everyone! The human race! Half a century ago, we walked on the moon. But now, we have nothing, can't change anything!"

Camille marched over to them holding a stack of paper. Cheng Xin guessed that it was the interim report on the feasibility of the Staircase Program. Camille held up the document for a few seconds, but instead of handing it over to either of them, she slammed it against the ground.

Cheng Xin bent down and picked up the document. Indeed, it was the interim feasibility report. She and Vadimov flipped through it, but it was highly technical and difficult to skim. Wade had also returned to their circle -- the PDC secretary had informed him that the session would begin in fifteen minutes.

Camille calmed down a bit in the presence of the PIA chief. "NASA has conducted two small tests of nuclear pulse propulsion in space, and you can read the results in the report. Basically, our proposed spacecraft is still too heavy to reach the required speed. They calculate the entire assembly needs to be one-twentieth its proposed mass. One-twentieth! That's ten kilograms!

"But wait, they also sent us some good news. The sail, it turns out, can be reduced to under ten kilograms. They took pity on us and told us that we can have an effective payload of half a kilogram. But that is the absolute limit, because any increase in the payload will require thicker cables for attachment to the sail. Every additional gram in the payload means three more grams of cables. Thus, we're stuck with zero point five kilograms. Haha, it's just like our angel predicted: light as a feather!"

Wade smiled. "We should ask Monnier, my mother's kitten, to go. Though, even she would have to lose half of her weight."

Whenever others were happily absorbed by their work, Wade appeared gloomy; when others were forlorn, he became relaxed and jokey. Initially, Cheng Xin had attributed this quirk to part of his leadership style. But Vadimov told her that she didn't know how to read people. Wade's behavior had nothing to do with his leadership style or rallying the troops -- he just enjoyed watching others lose hope, even if he himself was among those who ought to be in despair. He took pleasure in the desperation of others. Cheng Xin had been surprised that Vadimov, who always tried to speak of others generously, held such an opinion of Wade. But right now, it did look as though Wade took pleasure in watching the three of them suffer.

"You, and you," Wade said, pointing to Camille and Cheng Xin. "You're not allowed to lose control like this in the future. You must advance, stop at nothing to advance!"

For the first time, Cheng Xin refused to obey an order from him. She remained on the ground. "I'm tired." Her voice was wooden.

"Of course not."

"There's no way forward," said Vadimov. "We have to give up."

Cheng Xin felt weak. Days of exhaustion hit her at once, and she sank to the lawn.

Vadimov's and Camille's eyes brightened. Cheng Xin also seemed to have recovered her strength. She stood up.

"Get up," said Wade.

"No, we should proceed as though nothing has happened. But we can't prepare new documents, so we have to orally present the new plan."

Accompanied by military escort vehicles and helicopters, an ambulance departed with the Fourth Wallfacer. Against the lights of New York City, Wade's figure appeared as a black ghost, his eyes glinting with a cold light.

"What new plan? A five-hundred-gram cat?"

"What about the PDC session? Cancel it?"

"The reason you think there's no path forward is because you don't know how to disregard the consequences."

In fourteenth-century China, during the Ming Dynasty, the Chinese navy invented a weapon called Huolong Chu Shui, literally meaning "fiery dragon issuing from water." This was a multistage gunpowder rocket similar in principle to antiship missiles of the Common Era. The missile itself (Huolong) was augmented with booster rockets. When launched, the booster rockets propelled the missile toward the enemy ship by flying just above the surface of the water. As the booster rockets burnt out, they ignited a cluster of smaller rocket arrows stored inside the missile, and these would shoot out the front, causing massive damage to enemy ships.

Ancient warfare also saw the use of repeating crossbows, which prefigured Common Era machine guns. These appeared in both the West and the East, and Chinese versions have been discovered in tombs dating from the fourth century B. C.

Excerpt from A Past Outside of Time, The Staircase Program

Both of these weapon systems were attempts to utilize primitive technology in novel ways that demonstrated a power incongruous for their time period.

"We'll send only a brain," he said.

Every bomb had to detonate just as the radiation sail passed it. The distance from each bomb to the sail at the moment of the explosion ranged from three thousand to ten thousand meters, depending on the bomb's yield. As the probe's velocity increased, the timing needed to be more precise. However, even as the sail's speed reached 1 percent of lightspeed, the margin for error remained above the nanosecond range, well achievable by the technology of the time.

At the time of the Staircase Program, humans had already successfully launched a few spacecraft outside the Solar System and had managed to land probes on Neptunian satellites. Thus, the requisite technology to distribute nuclear bombs along the acceleration leg of the probe's course was relatively mature. But controlling the flight path of the probe to pass by each bomb, and detonating each at the precise moment, posed great technical challenges.

Looking back, the Staircase Program implemented at the beginning of the Crisis Era was a similar advance. Using only the primitive technology available at the time, it managed to boost a small probe to 1 percent of lightspeed. This achievement should have been impossible without technology that would not appear for another one and a half centuries.

The probe itself contained no engine. Its direction was entirely determined by the relative positions of the detonating bombs. Each bomb along the route was equipped with small positional thrusters. As the sail passed each bomb, the distance between them was only a few hundred meters. By adjusting this distance, it was possible to alter the angle between the sail and the propulsive force generated by the nuclear explosion, and thus control the direction of flight.

The radiation sail was a thin film, and the only way to carry the payload was to drag it behind in a capsule. The entire probe thus resembled a giant parachute -- except that the parachute flew "upwards." To avoid damage to the payload from the nuclear explosions occurring three to ten kilometers behind the sail, the cables connecting the sail to the payload had to be very long: about five hundred kilometers. An ablative layer protected the payload capsule itself. As the nuclear bombs exploded, the ablative material gradually vaporized, cooling the capsule as well as lowering the total mass.

The mass launch of Peacekeeper missiles had been in process for over half an hour. Trails from six missiles merged together, and, lit up by the moon, resembled a silvery road that reached into heaven.

Of course, Huolong Chu Shui was not, in fact, equivalent to a two-stage rocket, and the repeating crossbow was not the same as a machine gun. Similarly, the Staircase Program could not bring about a new Space Age. It was only a desperate attempt that drew upon everything humanity's primitive level of technology could offer.

Crisis Era, Years 1-4, Cheng Xin

The cables were made from a nanomaterial called "Flying Blade." Only about a tenth of the thickness of a strand of spider silk, the cables were invisible to the naked eye. Eight grams of the material could be stretched into a cable one hundred kilometers long, yet it was strong enough to securely pull the payload capsule during acceleration, and would not break from the massive radiation generated by the nuclear explosions.

Every five minutes, another fiery ball ascended this silvery road into the sky. Shadows cast by trees and people swept along the ground like the second hands of clocks. This first launch would involve thirty missiles, sending three hundred nuclear warheads with yields ranging from five hundred kilotons to 2.5 megatons into orbit.

The last session of the PDC marked the first time a resolution had been passed based on a proposal that wasn't even written down. And Cheng Xin got to witness the debating skills of Wade, usually a man of few words. He argued that if we assumed the Trisolarans were capable of reviving a body in deep freeze, then it made sense to assume they were also capable of reviving a bare brain in similar condition and conversing with it through an external interface. Surely such a task was trivial for a civilization capable of unfolding a proton into two dimensions and etching circuits over the resulting surface. In some sense, a brain was no different from the whole person: It possessed the person's thoughts, personality, and memories. And it most definitely possessed the person's capacity for stratagems. If successful, the brain would still be a ticking bomb in the heart of the enemy.

Cheng Xin's eyes filled with hot tears. Each ascending rocket lit them up like bright, glistening pools. She told herself again and again that no matter what happened next, it was worth it to have pushed the Staircase Program this far.

At the same time, in Russia and China, Topol and Dongfeng missiles were also rising into the sky. The scene resembled a doomsday scenario, but Cheng Xin could tell by the curvature of the rocket trails that these were orbital launches instead of intercontinental strikes. These devices, which could have killed billions, would never return to the surface of the Earth. They would pool their enormous power to accelerate a feather to 1 percent of the speed of light.

But the two men beside her, Vadimov and Wade, seemed unmoved by the spectacular scene playing out before them. They didn't even bother looking up; instead, they smoked and conversed in low voices. Cheng Xin knew very well what they were discussing: who would be chosen for the Staircase Program.

The other leaders and implementers of the Staircase Program did not suffer her pangs of guilt. If PIA were a national intelligence agency, this matter would have been resolved long ago. However, since PIA was only a joint intelligence committee formed by the permanent member nations of the PDC, after the Staircase Program was revealed to the international community, the issue became extremely sensitive.

Once the Staircase Program was approved, the problem of who should be sent came to the forefront. Cheng Xin lacked the courage to even imagine such a person. Even if his or her brain could be captured by the Trisolarans and revived, life afterwards -- if such an existence could be called life -- would be one interminable nightmare. Every time she thought about this, her heart felt squeezed by a hand chilled to minus-two-hundred-degrees Celsius.

Although the PDC members did not fully agree that a brain was the same as a whole person, they lacked better choices, especially since their interest in the Staircase Program was largely based on the technology for accelerating the probe to 1 percent of lightspeed. In the end, the resolution passed with five yeses and two abstentions.

After the initial panic of the Crisis subsided, a mainstream consensus gradually dominated international politics: It was important to prevent the Crisis from being leveraged as a tool to destroy democracy. PIA personnel were instructed by their respective nations to be extra careful during the process of selecting potential Staircase Program subjects and not commit political errors that would embarrass their countries.

The key problem was this: Before launch, the subject would have to be killed.

Once again, Wade came up with a unique solution to the difficulty: advocating, through the PDC and then the UN, the passage of euthanasia laws in as many countries as possible. But even he wasn't confident that this plan would work.

Of the seven permanent members of the PDC, three quickly passed euthanasia laws. But these laws all clearly provided that euthanasia was only available to those suffering terminal illnesses. This was not ideal for the Staircase Program, but it seemed the outer boundary of political acceptability.

Thus, candidates for the Staircase Program had to be chosen from the population of terminally ill patients.

When she went to see Chief Wade to give a status report, her happiness was so palpable that Wade asked her what the matter was with her. She showed him the deed.

The thunderous noises and bright lights in the sky faded. The missile launches had come to an end. Wade and a few other PDC observers got into their cars and left, leaving only Vadimov and Cheng Xin.

Four days ago, Cheng Xin had received the deed to DX3906. She was utterly surprised and fell into a delirium of joy. For a whole day, she kept on repeating to herself: Someone gave me a star; someone gave me a star; someone gave me a star…

"Why don't we take a look at your star?" he said.

But Cheng Xin wasn't bothered by his cynicism -- she had already known what he was going to say. She knew very little about Wade except his work history: service in the CIA, then deputy secretary of Homeland Security, and finally here. As for his personal life, other than the fact that he had a mother and his mother had a kitten, she knew nothing. No one else did, either. She didn't even know where he lived. He was like a machine: When he wasn't working, he was shut down somewhere unknown.

"A useless piece of paper," he said, and handed it back to her. "If you're smart, you should drop the price and resell it right away. Otherwise you'll end up with nothing."

She couldn't help but bring up the star to Vadimov, who enthusiastically congratulated her. "Every girl in the world must be jealous," he said. "Including all living women and dead princesses. You're certainly the first woman in the history of humankind to be given a star." For a woman, was there any greater happiness than to be given a star by someone who loved her?

Cheng Xin sighed as well. A much younger Cheng Xin had once indulged in rose-tinted fantasies that the Cheng Xin of the present would mock. This real star that appeared out of nowhere, however, far exceeded those romantic dreams.

"But who is he?" Cheng Xin muttered.

"Shouldn't be hard to guess. He must be rich, for one thing. He just spent a few million on a symbolic gift."

"He's also a cultured soul. Stands apart from the crowd." Vadimov sighed. "And he just made a romantic gesture that I'd call fucking ridiculous if I read it in a book or saw it in a movie."

Cheng Xin shook her head. She'd had many admirers and suitors, but none of them were that wealthy.

Maybe it was a secret admirer from afar who, on impulse, decided to use a tiny part of his vast wealth to indulge in a bit of whimsy, to satisfy some desire she would never understand. Even so, she was grateful.

She was certain that she knew no man like that.

That night, Cheng Xin climbed onto the top of One World Trade Center, eager to see her new star. She had carefully reviewed the materials that accompanied the deed explaining how to find it. But the sky in New York was overcast. The next day and the day after were the same. The clouds formed a giant teasing hand that covered her gift, refusing to let go. But Cheng Xin wasn't disappointed; she knew she had received a gift that couldn't be taken away. DX3906 was in this universe, and it might even outlast the Earth and the Sun. She would see it, one day.

She stood on the balcony of her apartment at night, gazing up at the sky and imagining her star. The lights of the city below cast a dim yellow glow against the cloud cover, but she imagined her star giving the clouds a rosy glow.

In her dream, she flew over the star's surface. It was a rose-colored sphere, but instead of scorching flames, she felt the coolness of a spring breeze. Below her was the clear water of an ocean, through which she could see swaying, rose-colored clouds of algae…

The trails left behind by the missiles gradually faded against the clear night sky. Cheng Xin and Vadimov reviewed the observation guide for her star. Both had had some training in astronomy, and soon they were looking at the approximate location. But neither could see it.

Vadimov took out two pairs of military-issue binoculars. With them, it was easy to see DX3906. After that, even without the binoculars, they could find the star. Cheng Xin stared at the faint red dot, mesmerized, struggling to comprehend the unimaginable distance between them, struggling to translate the distance into terms that could be grasped by the human mind.

After she woke up, she laughed at herself. As an aerospace professional, even in her dreams she couldn't forget that DX3906 had no planets.

On the fourth day after she received the star, Cheng Xin and a few other PIA employees flew to Cape Canaveral to attend the launch ceremony for the first batch of missiles. Achieving orbit required taking advantage of the Earth's spin, and the ICBMs had been moved here from their original deployment bases.

"If you put my brain on the Staircase Program probe and launched it at the star, it would take thirty thousand years to get there."

"Have you been pressured?" Cheng Xin was thinking of Wade.

"What's wrong?"

"What are you talking about?"

"Sure. But I'm still running from my responsibility."

After a momentary shock, Cheng Xin realized that Vadimov was right: He had extensive experience in spaceflight, diplomacy, and intelligence; he was steady and mature… Even if they were able to expand the pool of candidates to include healthy individuals, Vadimov would still be the best choice.

"But you're healthy."

"No, but I know what I must do; I just haven't done it. I got married three years ago, and my daughter just turned one. I'm not afraid to die, but my family matters to me. I don't want them to see me turned into something worse than a corpse."

Cheng Xin heard no response. When she turned around, she saw that Vadimov was no longer looking at the star with her, but leaning against the car and looking at nothing. She could see that his face was troubled.

Vadimov was silent for some time. "I've been avoiding my duty."

"I'm the best candidate for the Staircase Program."

"Yes, but I wanted to tell you… in the end, I'm the best candidate."

"You don't have to do this. Neither the PIA nor your government has ordered you to do this, and they can't!"

"Mikhail, humankind isn't just some abstraction. To love humanity, you must start by loving individual persons, by fulfilling your responsibility to those you love. It would be absurd to blame yourself for it."

The process of selecting a subject for the Staircase Program was fully underway, but the effort imposed little direct pressure on Cheng Xin. She was asked to perform some basic tasks such as examining candidates' knowledge of spaceflight, a primary requirement. Since the pool of candidates was limited to terminally ill patients, it was almost impossible to find someone with the requisite expertise. The PIA intensified efforts to identify more candidates through every available channel.

"Thank you, Cheng Xin. You deserve your gift." Vadimov looked up at Cheng Xin's star. "I would love to give my wife and daughter a star."

A bright point of light appeared in the sky, then another. Their glow cast shadows on the ground. They were testing nuclear pulse propulsion in space.

Cheng Xin needed to return to China for business. Since she was Tianming's classmate, Assistant Chief Yu asked her to represent the PIA and discuss the matter with Tianming. She agreed, still not thinking much of it.

For the rest of her life, Cheng Xin would remember that moment. Every time, she had to admit to herself that she just didn't think much about Tianming as a person.

One of Cheng Xin's college classmates came to New York to visit her. The talk turned to what had happened to others in their class, and her friend mentioned Yun Tianming. She had heard from Hu Wen that Tianming was in the late stages of lung cancer and didn't have much time left. Right away, Cheng Xin went to Assistant Chief Yu to suggest Tianming as a candidate.

After hearing Cheng Xin's story, Tianming slowly sat up on the bed. Cheng Xin asked him to lie down, but he said he wanted to be by himself for a while.

Cheng Xin closed the door lightly behind her. Tianming began to laugh hysterically.

What a fucking idiot I am! Did I think that because I gave her a star out of love, she would return that love? Did I think that she had flown across the Pacific to save me with her saintly tears? What kind of fairy tale have I been telling myself?

No, Cheng Xin had come to ask him to die.

He made another logical deduction that made him laugh even harder, until it was hard to breathe. Based on Cheng Xin's timing, she could not know that he had already chosen euthanasia. In other words, if Tianming hadn't already chosen this path, she would try to convince him to take it. Maybe she would even entice him, or pressure him, until he agreed.

Euthanasia meant "good death," but there was nothing good about the fate she had in mind for him.

Cheng Xin wanted a part of him, the part that carried his soul, to wander forever in that frigid, endless, lightless abyss.

His sister had wanted him to die because she thought money was being wasted. He could understand that -- and he believed that she genuinely wanted him to die in peace. Cheng Xin, on the other hand, wanted him to suffer in eternity. Tianming was terrified of space. Like everyone who studied spaceflight for a living, he understood space's sinister nature better than the general public. Hell was not on Earth, but in heaven.

Then they would search his memory to identify what forms of suffering he feared the most. They would discover a torture technique he had once read in a history book -- first, the victim was whipped until not an inch of his skin remained intact; then the victim's body was tightly wrapped in bandages; and after the victim had stopped bleeding, the bandages would be torn off, ripping open all the wounds at once -- then send signals replicating such torture into his brain. The victim in his history book couldn't live for long in those conditions, but Tianming's brain would not be able to die. The most that could happen was that his brain could shut down from shock. In the eyes of Trisolarans, it would resemble a computer locking up. They'd just restart his brain and run another experiment, driven by curiosity, or merely the desire for entertainment…

If the Trisolarans were to really capture his brain as Cheng Xin wished, then his true nightmare would begin. Aliens who shared nothing with humanity would attach sensors to his brain and begin tests involving the senses. They would be most interested in the sensation of pain, of course, and so, by turn, he would experience hunger, thirst, whipping, burning, suffocation, electric shocks, medieval torture techniques, death by a thousand cuts…

Actually, that would be the best outcome.

Cheng Xin opened the door. "Tianming, what's wrong?"

He would have no escape. Without hands or body, he would have no way to commit suicide. His brain would resemble a battery, recharged again and again with pain. There would be no end.

He choked off his laugh and turned still as a corpse.

He howled with laughter.

He gazed at her face, at her solemn but eager expression. She was fighting for humanity, for Earth… But what was wrong with the scene all around him? The light of the setting sun coming through the window fell against the wall like a pool of blood; the lonesome oak tree outside the window appeared as skeletal arms rising out of the grave…

"Tianming, on behalf of the UN-PDC Strategic Intelligence Agency, I ask you whether you're willing to shoulder your responsibility as a member of the human race and accept this mission. This is entirely voluntary. You are free to say no."

The hint of a smile -- an agonized, melancholic smile -- appeared at the corners of his mouth. Gradually, the smile spread to the rest of his face.

"Of course. I accept," he said.