Langdon sat white-knuckled in the passenger seat, twisted backward, scanning behind them for any signs of the police. He suddenly wished he had not decided to run. You didn't, he reminded himself.

Sophie had made the decision for him when she threw the GPS dot out the bathroom window.

Behind the wheel Sophie was fishing in her sweater pocket. She removed a small metal object and held it out for him. "Robert, you'd better have a look at this. This is what my grandfather left me behind Madonna of the Rocks."

Now, as they sped away from the embassy, serpentining through sparse traffic on Champs-Elysées, Langdon felt his options deteriorating. Although Sophie seemed to have lost the police, at least for the moment, Langdon doubted their luck would hold for long.

Feeling a shiver of anticipation, Langdon took the object and examined it. It was heavy and shaped like a cruciform. His first instinct was that he was holding a funeral pieu -- a miniature version of a memorial spike designed to be stuck into the ground at a gravesite. But then he noted the shaft protruding from the cruciform was prismatic and triangular. The shaft was also pockmarked with hundreds of tiny hexagons that appeared to be finely tooled and scattered at random.

Sophie's SmartCar tore through the diplomatic quarter, weaving past embassies and consulates, finally racing out a side street and taking a right turn back onto the massive thoroughfare of Champs-Elysées.

"Look at the other side," she said, changing lanes and sailing through an intersection.

When Langdon turned the key, he felt his jaw drop. There, intricately embossed on the center of the cross, was a stylized fleur-de-lis with the initials P. S.! "Sophie," he said, "this is the seal I told you about! The official device of the Priory of Sion." She nodded. "As I told you, I saw the key a long time ago. He told me never to speak of it again."

"It's a laser-cut key," Sophie told him. "Those hexagons are read by an electric eye." A key? Langdon had never seen anything like it.

Langdon's eyes were still riveted on the embossed key. Its high-tech tooling and age-old symbolism exuded an eerie fusion of ancient and modern worlds.

What an ancient brotherhood was doing with a futuristic key, Langdon had no idea. The Priory existed for the sole purpose of protecting a secret. A secret of incredible power. Could this key have something to do with it? The thought was overwhelming. "Do you know what it opens?"

"He told me the key opened a box where he kept many secrets."

Langdon felt a chill to imagine what kind of secrets a man like Jacques Saunière might keep.

"It looks Christian," Sophie pressed.

Sophie looked disappointed. "I was hoping you knew."

Langdon was not so sure about that. The head of this key was not the traditional long-stemmed Christian cross but rather was a square cross -- with four arms of equal length -- which predated Christianity by fifteen hundred years. This kind of cross carried none of the Christian connotations of crucifixion associated with the longer-stemmed Latin Cross, originated by Romans as a torture device. Langdon was always surprised how few Christians who gazed upon 'the crucifix" realized their symbol's violent history was reflected in its very name: "cross" and "crucifix" came from the Latin verb cruciare -- to torture.

Langdon remained silent as he turned the cruciform in his hand, examining it.

"Sophie," he said, "all I can tell you is that equal-armed crosses like this one are considered peaceful crosses. Their square configurations make them impractical for use in crucifixion, and their balanced vertical and horizontal elements convey a natural union of male and female, making them symbolically consistent with Priory philosophy." She gave him a weary look. "You have no idea, do you?"

Langdon frowned. "Not a clue."

"Okay, we have to get off the road." Sophie checked her rearview mirror. "We need a safe place to figure out what that key opens." Langdon thought longingly of his comfortable room at the Ritz. Obviously, that was not an option.

"You must know people. You live here."

"How about my hosts at the American University of Paris?"

"Too obvious. Fache will check with them."

"Fache will run my phone and e-mail records, talk to my coworkers. My contacts are compromised, and finding a hotel is no good because they all require identification." Langdon wondered again if he might have been better off taking his chances letting Fache arrest him at the Louvre. "Let's call the embassy. I can explain the situation and have the embassy send someone to meet us somewhere."

"Meet us?" Sophie turned and stared at him as if he were crazy.

"Robert, you're dreaming. Your embassy has no jurisdiction except on their own property. Sending someone to retrieve us would be considered aiding a fugitive of the French government. It won't happen. If you walk into your embassy and request temporary asylum, that's one thing, but asking them to take action against French law enforcement in the field?" She shook her head. "Call your embassy right now, and they are going to tell you to avoid further damage and turn yourself over to Fache. Then they'll promise to pursue diplomatic channels to get you a fair trial." She gazed up the line of elegant storefronts on Champs-Elysées. "How much cash do you have?"

"Credit cards?"

"Of course."

Sophie gunned the SmartCar into the rotary. "Trust me."

Langdon made no response. Trust had not gotten him very far this evening. Pulling back the sleeve of his jacket, he checked his watch -- a vintage, collector's-edition Mickey Mouse wristwatch that had been a gift from his parents on his tenth birthday. Although its juvenile dial often drew odd looks, Langdon had never owned any other watch; Disney animations had been his first introduction to the magic of form and color, and Mickey now served as Langdon's daily reminder to stay young at heart.

Langdon checked his wallet. "A hundred dollars. A few euro. Why?"

As Sophie accelerated, Langdon sensed she was formulating a plan. Dead ahead, at the end of Champs-Elysées, stood the Arc de Triomphe -- Napoleon's 164-foot-tall tribute to his own military potency -- encircled by France's largest rotary, a nine-lane behemoth.

Sophie's eyes were on the rearview mirror again as they approached the rotary. "We lost them for the time being," she said, "but we won't last another five minutes if we stay in this car." So steal a different one, Langdon mused, now that we're criminals. "What are you going to do?"

"I imagine it would have to be." She gave him a quick smile and exited the rotary, heading due north, away from the city center.

At the moment, however, Mickey's arms were skewed at an awkward angle, indicating an equally awkward hour. 2:51 A. M.

"Long story," he said, pulling his sleeve back down.

"Interesting watch," Sophie said, glancing at his wrist and maneuvering the SmartCar around the wide, counterclockwise rotary.

Barely making two green lights, she reached the third intersection and took a hard right onto Boulevard Malesherbes. They'd left the rich, tree-lined streets of the diplomatic neighborhood and plunged into a darker industrial neighborhood. Sophie took a quick left, and a moment later, Langdon realized where they were.

Ahead of them, the glass-roofed train terminal resembled the awkward offspring of an airplane hangar and a greenhouse. European train stations never slept. Even at this hour, a half-dozen taxis idled near the main entrance. Vendors manned carts of sandwiches and mineral water while grungy kids in backpacks emerged from the station rubbing their eyes, looking around as if trying to remember what city they were in now. Up ahead on the street, a couple of city policemen stood on the curb giving directions to some confused tourists.

Gare Saint-Lazare.

Sophie pulled her SmartCar in behind the line of taxis and parked in a red zone despite plenty of legal parking across the street. Before Langdon could ask what was going on, she was out of the car. She hurried to the window of the taxi in front of them and began speaking to the driver.

Sophie was already heading for the train station entrance. "Come on. We're buying two tickets on the next train out of Paris."

"What happened?" Langdon demanded, joining Sophie on the curb as the taxi disappeared.

As Langdon got out of the SmartCar, he saw Sophie hand the taxi driver a big wad of cash. The taxi driver nodded and then, to Langdon's bewilderment, sped off without them.

Langdon hurried along beside her. What had begun as a one-mile dash to the U. S. Embassy had now become a full-fledged evacuation from Paris. Langdon was liking this idea less and less.