The security alarm on the west end of the Denon Wing sent the pigeons in the nearby Tuileries Gardens scattering as Langdon and Sophie dashed out of the bulkhead into the Paris night. As theyran across the plaza to Sophie's car, Langdon could hear police sirens wailing in the distance.

Langdon had barely thrown himself into the passenger seat before Sophie gunned the SmartCar up and over a curb onto a gravel divider. He gripped the dash as the car shot out across a sidewalk and bounced back down over into the small rotary at Carrousel du Louvre.

She's kidding, right? The vehicle was easily the smallest car Langdon had ever seen.

For an instant, Sophie seemed to consider taking the shortcut across the rotary by plowing straight ahead, through the median's perimeter hedge, and bisecting the large circle of grass in the center.

"That's it there," Sophie called, pointing to a red snub-nosed two-seater parked on the plaza.

"SmartCar," she said. "A hundred kilometers to the liter."

"No!" Langdon shouted, knowing the hedges around Carrousel du Louvre were there to hide the perilous chasm in the center -- La Pyramide Inversée -- the upside-down pyramid skylight he had seen earlier from inside the museum. It was large enough to swallow their Smart-Car in a single gulp. Fortunately, Sophie decided on the more conventional route, jamming the wheel hard to the right, circling properly until she exited, cut left, and swung into the northbound lane, accelerating toward Rue de Rivoli.

The two-tone police sirens blared louder behind them, and Langdon could see the lights now in his side view mirror. The SmartCar engine whined in protest as Sophie urged it faster away from the Louvre. Fifty yards ahead, the traffic light at Rivoli turned red. Sophie cursed under her breath and kept racing toward it. Langdon felt his muscles tighten.

"Sophie?"

Slowing only slightly as they reached the intersection, Sophie flicked her headlights and stole a quick glance both ways before flooring the accelerator again and carving a sharp left turn through the empty intersection onto Rivoli.

As they straightened out, Langdon turned in his seat, craning his neck to look out the rear window toward the Louvre. The police did not seem to be chasing them. The sea of blue lights was assembling at the museum.

Accelerating west for a quarter of a mile, Sophie banked to the right around a wide rotary. Soon they were shooting out the other side onto the wide avenue of Champs-Elysées.

His heartbeat finally slowing, Langdon turned back around. "That was interesting."

Sophie's quick thinking had been impressive.

Sophie didn't seem to hear. Her eyes remained fixed ahead down the long thoroughfare of Champs-Elysées, the two-mile stretch of posh storefronts that was often called the Fifth Avenue of Paris.

Madonna of the Rocks.

The embassy was only about a mile away, and Langdon settled into his seat.

Sophie had said her grandfather left her something behind the painting. A final message? Langdon could not help but marvel over Saunière's brilliant hiding place; Madonna of the Rocks was yet another fitting link in the evening's chain of interconnected symbolism. Saunière, it seemed, at every turn, was reinforcing his fondness for the dark and mischievous side of Leonardo da Vinci.

So dark the con of man.

Da Vinci's original commission for Madonna of the Rocks had come from an organization known as the Confraternity of the Immaculate Conception, which needed a painting for the centerpiece of an altar triptych in their church of San Francesco in Milan. The nuns gave Leonardo specific dimensions, and the desired theme for the painting -- the Virgin Mary, baby John the Baptist, Uriel, and Baby Jesus sheltering in a cave. Although Da Vinci did as they requested, when he delivered the work, the group reacted with horror. He had filled the painting with explosive and disturbing details.

Opposite Mary sat Uriel, also with an infant, presumably baby John the Baptist. Oddly, though, rather than the usual Jesus-blessing-John scenario, it was baby John who was blessing Jesus… and Jesus was submitting to his authority! More troubling still, Mary was holding one hand high above the head of infant John and making a decidedly threatening gesture -- her fingers looking like eagle's talons, gripping an invisible head. Finally, the most obvious and frightening image: Just below Mary's curled fingers, Uriel was making a cutting gesture with his hand -- as if slicing the neck of the invisible head gripped by Mary's claw-like hand.

Langdon's students were always amused to learn that Da Vinci eventually mollified the confraternity by painting them a second, "watered-down" version of Madonna of the Rocks in which everyone was arranged in a more orthodox manner. The second version now hung in London's National Gallery under the name Virgin of the Rocks, although Langdon still preferred the Louvre's more intriguing original.

The painting showed a blue-robed Virgin Mary sitting with her arm around an infant child, presumably Baby Jesus.

Her eyes remained on the road. "I'll show you once we're safely inside the embassy."

As Sophie gunned the car up Champs-Elysées, Langdon said, "The painting. What was behind it?"

"You'll show it to me?" Langdon was surprised. "He left you a physical object?"

We're going to make it, Sophie thought as she swung the SmartCar's wheel to the right, cutting sharply past the luxurious H. tel de Crillon into Paris's tree-lined diplomatic neighborhood. The embassy was less than a mile away now. She was finally feeling like she could breathe normally again.

Sophie gave a curt nod. "Embossed with a fleur-de-lis and the initials P. S."

Langdon couldn't believe his ears.

Although the key barely had entered Sophie's thoughts through the years, her work in the intelligence community had taught her plenty about security, and now the key's peculiar tooling no longer looked so mystifying. A laser-tooled varying matrix. Impossible to duplicate. Rather than teeth that moved tumblers, this key's complex series of laser-burned pockmarks was examined by an electric eye. If the eye determined that the hexagonal pockmarks were correctly spaced, arranged, and rotated, then the lock would open.

Even as she drove, Sophie's mind remained locked on the key in her pocket, her memories of seeing it many years ago, the gold head shaped as an equal-armed cross, the triangular shaft, the indentations, the embossed flowery seal, and the letters P. S.

Sophie could not begin to imagine what a key like this opened, but she sensed Robert would be able to tell her. After all, he had described the key's embossed seal without ever seeing it. The cruciform on top implied the key belonged to some kind of Christian organization, and yet Sophie knew of no churches that used laser-tooled varying matrix keys.

When she arrived at their Paris home, however, her grandfather was not there. Disappointed, she knew he had not been expecting her and was probably working at the Louvre. But it's Saturday afternoon, she realized. He seldom worked on weekends. On weekends, he usually -- Grinning, Sophie ran out to the garage. Sure enough, his car was gone. It was the weekend. Jacques Saunière despised city driving and owned a car for one destination only -- his vacation chateau in Normandy, north of Paris. Sophie, after months in the congestion of London, was eager for the smells of nature and to start her vacation right away. It was still early evening, and she decided to leave immediately and surprise him. Borrowing a friend's car, Sophie drove north, winding into the deserted moon-swept hills near Creully. She arrived just after ten o'clock, turning down the long private driveway toward her grandfather's retreat. The access road was over a mile long, and she was halfway down it before she could start to see the house through the trees -- a mammoth, old stone chateau nestled in the woods on the side of a hill.

Sophie had witnessed proof of that ten years ago. Ironically, it had been another key -- a far more normal one -- that had revealed his true nature to her.

The afternoon had been warm when she landed at Charles de Gaulle Airport and hailed a taxi home. Grand-père will be so surprised to see me, she thought. Returning from graduate school in Britain for spring break a few days early, Sophie couldn't wait to see him and tell him all about the encryption methods she was studying.

Besides, my grandfather was no Christian…

She knocked. Nobody answered. Puzzled, she walked around and tried the back door. It too was locked. No answer.

Sophie had half expected to find her grandfather asleep at this hour and was excited to see the house twinkling with lights. Her delight turned to surprise, however, when she arrived to find the driveway filled with parked cars -- Mercedeses, BMWs, Audis, and a Rolls-Royce.

Sophie stared a moment and then burst out laughing. My grand-père, the famous recluse! Jacques Saunière, it seemed, was far less reclusive than he liked to pretend. Clearly he was hosting a party while Sophie was away at school, and from the looks of the automobiles, some of Paris's most influential people were in attendance.

No music.

Confused, she stood a moment and listened. The only sound she heard was the cool Normandy air letting out a low moan as it swirled through the valley.

No voices.

In the silence of the woods, Sophie hurried to the side of the house and clambered up on a woodpile, pressing her face to the living room window.

Nothing.

Eager to surprise him, she hurried to the front door. When she got there, though, she found it locked.

What she saw inside made no sense at all.

"Nobody's here!" The entire first floor looked deserted.

Where are all the people?

Heart racing, Sophie ran to the woodshed and got the spare key her grandfather kept hidden under the kindling box. She ran to the front door and let herself in. As she stepped into the deserted foyer, the control panel for the security system started blinking red -- a warning that the entrant had ten seconds to type the proper code before the security alarms went off.

He has the alarm on during a party?

Sophie quickly typed the code and deactivated the system.

Sophie could not imagine. Crouching, she put her ear to the floor and listened. Yes, the sound was definitely coming from below. The voices seemed to be singing, or… chanting? She was frightened. Almost more eerie than the sound itself was the realization that this house did not even have a basement.

Entering, she found the entire house uninhabited. Upstairs too. As she descended again to the deserted living room, she stood a moment in the silence, wondering what could possibly be happening.

It was then that Sophie heard it.

Muffled voices. And they seemed to be coming from underneath her.

Walking toward the bare wooden wall, Sophie sensed the chanting getting louder. Hesitant, she leaned her ear against the wood. The voices were clearer now. People were definitely chanting… intoning words Sophie could not discern.

The space behind this wall is hollow!

At least none I've ever seen.

Feeling around the edge of the panels, Sophie found a recessed finger hold. It was discreetly crafted. A sliding door. Heart pounding, she placed her finger in the slot and pulled it. With noiseless precision, the heavy wall slid sideways. From out of the darkness beyond, the voices echoed up.

Turning now and scanning the living room, Sophie's eyes fell to the only object in the entire house that seemed out of place -- her grandfather's favorite antique, a sprawling Aubusson tapestry. It usually hung on the east wall beside the fireplace, but tonight it had been pulled aside on its brass rod, exposing the wall behind it.

Sophie slipped through the door and found herself on a rough-hewn stone staircase that spiraled downward. She'd been coming to this house since she was a child and yet had no idea this staircase even existed!

Holding her breath, Sophie inched down another few steps and crouched down to look. It took her several seconds to process what she was seeing.

The room was a grotto -- a coarse chamber that appeared to have been hollowed from the granite of the hillside. The only light came from torches on the walls. In the glow of the flames, thirty or so people stood in a circle in the center of the room.

Beyond it, she could see a small patch of the basement floor -- stone, illuminated by the flickering orange blaze of firelight.

As she descended, the air grew cooler. The voices clearer. She heard men and women now. Her line of sight was limited by the spiral of the staircase, but the last step was now rounding into view.

Everyone in the room was wearing a mask. The women were dressed in white gossamer gowns and golden shoes. Their masks were white, and in their hands they carried golden orbs. The men wore long black tunics, and their masks were black. They looked like pieces in a giant chess set.

I'm dreaming, Sophie told herself. A dream. What else could this be?

Everyone in the circle rocked back and forth and chanted in reverence to something on the floor before them… something Sophie could not see.

Overtaken by nausea, Sophie spun, clutching at the stone walls as she clambered back up the stairs.

I WAS THERE. DON'T TRY TO FIND ME.

Pulling the door closed, she fled the deserted house, and drove in a tearful stupor back to Paris.

That night, with her life shattered by disillusionment and betrayal, she packed her belongings and left her home. On the dining room table, she left a note.

Beside the note, she laid the old spare key from the chateau's woodshed.

The chanting grew steady again. Accelerating. Thundering now. Faster. The participants took a step inward and knelt. In that instant, Sophie could finally see what they all were witnessing. Even as she staggered back in horror, she felt the image searing itself into her memory forever.

"Sophie!" Langdon's voice intruded. "Stop! Stop!"

Emerging from the memory, Sophie slammed on the brakes, skidding to a halt. "What? What happened?!"

Putting the SmartCar in reverse, she performed a composed three-point turn and reversed her direction. As she drove away, she heard the sound of squealing tires behind them. Sirens blared to life.

When she saw it, Sophie's blood went cold. A hundred yards ahead, the intersection was blocked by a couple of DCPJ police cars, parked askew, their purpose obvious. They've sealed off Avenue Gabriel!

Langdon gave a grim sigh. "I take it the embassy is off-limits this evening?"

Langdon pointed down the long street before them.

"Okay," Sophie, turn around very slowly.

Down the street, the two DCPJ officers who stood beside their cars were now staring in their direction, apparently curious about the headlights that had halted so abruptly up the street from them.

"Cursing," Sophie slammed down the accelerator.