Nights in Rome, like those in the desert, can be surprisingly cool, even after a warm day. Langdon was huddled now on the fringes of Piazza Navona, pulling his jacket around him. Like the distant white noise of traffic, a cacophony of news reports echoed across the city. He checked his watch. Fifteen minutes. He was grateful for a few moments of rest.

Piazza Navona. Fountain of the Four Rivers.

The piazza was deserted. Bernini's masterful fountain sizzled before him with a fearful sorcery. The foaming pool sent a magical mist upward, lit from beneath by underwater floodlights. Langdon sensed a cool electricity in the air.

The fountain's most arresting quality was its height. The central core alone was over twenty feet tall -- a rugged mountain of travertine marble riddled with caves and grottoes through which the water churned. The entire mound was draped with pagan figures. Atop this stood an obelisk that climbed another forty feet. Langdon let his eyes climb. On the obelisk's tip, a faint shadow blotted the sky, a lone pigeon perched silently.

A cross, Langdon thought, still amazed by the arrangement of the markers across Rome. Bernini'sFountain of the Four Rivers was the last altar of science. Only hours ago Langdon had been standing in the Pantheon convinced the Path of Illumination had been broken and he would never get this far. It had been a foolish blunder. In fact, the entire path was intact. Earth, Air, Fire, Water. And Langdon had followed it… from beginning to end.

Not quite to the end, he reminded himself. The path hadfive stops, not four. This fourth marker fountain somehow pointed to the ultimate destiny -- the Illuminati's sacred lair -- the Church of Illumination. Langdon wondered if the lair were still standing. He wondered if that was where the Hassassin had taken Vittoria.

Langdon found his eyes probing the figures in the fountain, looking for any clue as to the direction of the lair. Let angels guide you on your lofty quest. Almost immediately, though, he was overcome by an unsettling awareness. This fountain contained no angels whatsoever. It certainly contained none Langdon could see from where he was standing… and none he had ever seen in the past. The Fountain of the Four Rivers was a pagan work. The carvings were all profane -- humans, animals, even an awkward armadillo. An angel here would stick out like a sore thumb.

After making two complete circuits, the van banked inward toward Bernini's fountain. It pulled abreast of the basin, moving laterally along the rim until its side was flush with the fountain. Then it parked, its sliding door positioned only inches above the churning water.

Is this the wrong place? He considered the cruciform arrangement of the four obelisks. He clenched his fists. This fountain is perfect.

It was only 10:46P. M. when a black van emerged from the alleyway on the far side of the piazza. Langdon would not have given it a second look except that the van drove with no headlights. Like a shark patrolling a moonlit bay, the vehicle circled the perimeter of the piazza.

Mist billowed.

Langdon felt an uneasy premonition. Had the Hassassin arrived early? Had he come in a van? Langdon had imagined the killer escorting his last victim across the piazza on foot, like he had at St. Peter's, giving Langdon an open shot. But if the Hassassin had arrived in a van, the rules had just changed.

Langdon hunkered lower, crouched in the shadows beside the huge stairway leading up to the Church of St. Agnes in Agony. He gazed out at the piazza, his pulse climbing.

On the floor of the van, contorted in agony, lay a naked man. The man was wrapped in yards of heavy chains. He thrashed against the iron links, but the chains were too heavy. One of the links bisected the man's mouth like a horse's bit, stifling his cries for help. It was then that Langdon saw the second figure, moving around behind the prisoner in the dark, as though making final preparations.

Taking the gun, he slipped off his jacket and dropped it on the ground. He didn't want the added encumbrance of a tweed jacket, nor did he have any intention of taking Galileo'sDiagramma anywhere near the water. The document would stay here where it was safe and dry.

Suddenly, the van's side door slid open.

Langdon knew he had only seconds to act.

Langdon scrambled to his right. Circling the perimeter of the fountain, he positioned himself directly opposite the van. The fountain's massive centerpiece obscured his view. Standing, he ran directly toward the basin. He hoped the thundering water was drowning his footsteps. When he reached the fountain, he climbed over the rim and dropped into the foaming pool.

Waist-deep in water, Robert Langdon raised his gun and stepped out of the mist, feeling like some sort of aquatic cowboy making a final stand. "Don't move." His voice was steadier than the gun.

The Hassassin looked up. For a moment he seemed confused, as though he had seen a ghost. Then his lips curled into an evil smile. He raised his arms in submission. "And so it goes."

He reached the interior of the fountain and circled back to his left. He waded hard, clinging to the cover of the marble forms. Hiding himself behind the huge carved form of a horse, Langdon peered out. The van was only fifteen feet away. The Hassassin was crouched on the floor of the van, hands planted on the cardinal's chain-clad body, preparing to roll him out the open door into the fountain.

The water was waist deep and like ice. Langdon grit his teeth and plowed through the water. The bottom was slippery, made doubly treacherous by a stratum of coins thrown for good luck. Langdon sensed he would need more than good luck. As the mist rose all around him, he wondered if it was the cold or the fear that was causing the gun in his hand to shake.

Langdon motioned to the fountain. "I've come this far."

"The location has remained secret for centuries. Even to me it was only revealed recently. I would die before I break that trust."

Langdon stepped closer, his footing tentative beneath the water. The Hassassin looked remarkably calm, squatting there in the back of the van with his arms raised over his head. Langdon aimed at his chest, wondering if he should simply shoot and be done with it. No. He knows where Vittoria is. He knows where the antimatter is. I need information!

Langdon fought the urge to end it right there. "Where is she?"

"You look wet."

"Forget him. You've come for the woman. Do not pretend otherwise."

"So have many. The final step is the hardest."

Langdon felt his finger tighten on the trigger. The cardinal lay motionless now. He looked exhausted, moribund. "Untie him."

"You've already hesitated."

"I am eager to return to my prize."

The killer smiled. "You will never find its location."

"Get out of the van."

"I can find it without you."

She's alive. Langdon felt a ray of hope. "At the Church of Illumination?"

Langdon was incredulous. The lair is still standing. He aimed the gun. "Where?"

Langdon leveled the gun. "I won't hesitate to shoot."

"You're early."

"An arrogant thought."

"Somewhere safe. Awaiting my return."

The American was talking again. Probing. Maneuvering.

You had the advantage -- the element of surprise. You squandered it.

From the darkness of the van the Hassassin gazed out at his aggressor and couldn't help but feel an amused pity. The American was brave, that he had proven. But he was also untrained. That he had also proven. Valor without expertise was suicide. There were rules of survival. Ancient rules. And the American was breaking all of them.

The American was indecisive… hoping for backup most likely… or perhaps a slip of the tongue that would reveal critical information.

The killer almost laughed aloud. This is not one of your Hollywood movies… there will be no long discussions at gunpoint before the final shoot-out. This is the end. Now.

Never interrogate before you disable your prey. A cornered enemy is a deadly enemy.

Without breaking eye contact, the killer inched his hands across the ceiling of the van until he found what he was looking for. Staring dead ahead, he grasped it.

Then he made his play.

The two men splashed down in a spray of blood and water.

Langdon pulled the trigger, and the silencer spat. The bullet exploded through the toe of the Hassassin's left boot. Instantly Langdon felt the soles of the Hassassin's boots connect with his chest, driving him back with a crushing kick.

The motion was utterly unexpected. For an instant, Langdon thought the laws of physics had ceased to exist. The killer seemed to hang weightless in the air as his legs shot out from beneath him, his boots driving into the cardinal's side and launching the chain-laden body out the door. The cardinal splashed down, sending up a sheet of spray.

As the icy liquid engulfed Langdon's body, his first cognition was pain. Survival instinct came next. He realized he was no longer holding his weapon. It had been knocked away. Diving deep, he groped along the slimy bottom. His hand gripped metal. A handful of coins. He dropped them. Opening his eyes, Langdon scanned the glowing basin. The water churned around him like a frigid Jacuzzi.

Water dousing his face, Langdon realized too late what had happened. The killer had grasped one of the van's roll bars and used it to swing outward. Now the Hassassin was sailing toward him, feet-first through the spray.

You have the advantage, he told himself. You are in your element. Even in a soaked turtleneck Langdon was an agile swimmer. Water is your element.

Langdon realized even before he coasted over the cardinal's writhing body that he had grasped part of the metal chain that was weighing the man down. Langdon hovered a moment, immobilized by the sight of the terrified face staring up at him from the floor of the fountain.

Despite the instinct to breathe, fear kept him on the bottom. Always moving. He did not know from where the next assault would come. He needed to find the gun! His hands groped desperately in front of him.

When Langdon's fingers found metal a second time, he was certain his luck had changed. The object in his hand was no handful of coins. He gripped it and tried to pull it toward him, but when he did, he found himself gliding through the water. The object was stationary.

Jolted by the life in the man's eyes, Langdon reached down and grabbed the chains, trying to heave him toward the surface. The body came slowly… like an anchor. Langdon pulled harder. When the cardinal's head broke the surface, the old man gasped a few sucking, desperate breaths. Then, violently, his body rolled, causing Langdon to lose his grip on the slippery chains. Like a stone, Baggia went down again and disappeared beneath the foaming water.

Langdon dove, eyes wide in the liquid murkiness. He found the cardinal. This time, when Langdon grabbed on, the chains across Baggia's chest shifted… parting to reveal a further wickedness… a word stamped in seared flesh.

An instant later, two boots strode into view. One was gushing blood.