And then she realized why the forest ended.

It was the edge of a cliff.

And beyond was a waterfall. Directly ahead.

Terrified, Kate rolled over on her stomach, dug her fingers like claws into the mud, but to no avail. She still continued to slide. She couldn't stop. She rolled onto her back, still sliding down a chute of mud, helpless to do anything but watch the end coming, and then she shot out of the forest and was flying in the air, hardly daring to look down.

Almost immediately, she smashed down into foliage, clutched at it, and held. She swung up and down. She was in the branches of a large tree, hanging out over the cliff. The waterfall was directly below her. It wasn't as large as she had thought. Maybe ten, fifteen feet high. There was a pool at the base. She couldn't tell how deep it was.

She tried to climb back along the branches of the tree, but her hands were slippery from the mud. She kept slipping, twisting on the branch. Eventually, she was hanging beneath, clutching it with hands and legs like a sloth as she tried to work her way backward. She went another five feet, then realized she would never make it.

She fell.

She struck another branch, four feet lower. She hung there a moment, gripping the branch with slippery, muddy hands. Then she fell again, struck a lower branch.

Now she was just a few feet above the waterfall as it curved, roaring, over the lip of the cliff. The branches of the tree were wet from mist. She looked at the churning pool of water at the base. She couldn't see the bottom; she couldn't be sure how deep it was.

Hanging precariously from the branch, she thought: Where the hell is Chris? But in the next moment, she lost her grip and fell the rest of the way.

The water was an icy shock, bubbling, opaque, roiling furiously around her. She tumbled, disoriented, kicked to the surface, banged against rocks on the bottom. Finally, she came up beneath the waterfall, which pounded on her head with incredible force. She couldn't breathe. She ducked down again, swam ahead, and came out a few yards downstream. The water in the pool was calmer, though still chillingly cold.

She climbed out and sat on a rock. She saw that the churning water had washed all the mud from her clothes, from her body. She felt somehow new - and very glad to be alive.

Catching her breath, she looked around.

She was in a narrow little vale, the afternoon light misty from the waterfall. The valley was lush and wet, the grass was wet, the trees and rocks covered in moss. Directly ahead, a stone path led to a small chapel.

The chapel was wet, too, its surfaces covered with a kind of slimy mold, which streaked the walls and dripped from the edge of the roof. The mold was bright green.

The green chapel.

She also saw broken suits of armor heaped untidily beside the chapel door, old breastplates rusting in the pale sun and dented helmets lying on their sides; also swords and axes casually thrown all around.

Kate looked for Chris but didn't see him. Evidently, he hadn't fallen all the way, as she had. Probably he was now making his way down by another path. She thought she would wait for him; she had been happy to see him earlier, and missed him now. But she didn't see Chris anywhere. And aside from the waterfall, she heard no sound at all in the little valley, not even birds. It was ominously silent.

And yet she did not feel alone. She had the strong sense of something else here - a presence in the valley.

And then she heard a growling sound from inside the chapel: a guttural, animal sound.

She stood, and moved cautiously along the stone path toward the weapons. She picked up a sword and gripped the handle in both hands, even though she felt foolish; the sword was heavy, and she knew she had neither the strength nor the skill to use it. She was now close to the chapel door, and she smelled a strong odor of decay from inside. The growling came again.

And suddenly, an armored knight stepped forward, blocking the doorway. He was a huge man, nearly seven feet tall, and his armor was smeared with green mold. He wore a heavy helmet, so she could not see his face. He carried a heavy double-bladed ax, like an executioner's.

The ax swung back and forth as the knight advanced toward her.

Instinctively, she backed away, her eyes on the ax. Her first thought was to run, but the knight had jumped out at her quickly; she suspected he might be able to catch her. Anyway, she didn't want to turn her back on him. But she couldn't attack; he seemed to be twice her size. He never spoke; she heard only grunting and snarling from inside the helmet - animal sounds, demented sounds. He must be insane, she thought.

The knight came quickly closer, forcing her to act. She swung her sword with all her strength; he raised his ax to block and metal clanged against metal; her sword vibrated so strongly, she nearly lost her grip. She swung again, low, trying to cut his legs, but he easily blocked again, and with a quick twist of his ax, the blade flew out of her hands, landing on the grass beyond.

She turned and ran. Snarling, the knight raced forward and grabbed a fistful of her short hair. He dragged her, screaming, around to the side of the chapel. Her scalp burned; ahead, she saw a curved block of wood on the ground, showing the marks of many deep cuts. She knew what it was: a beheading block.

She was powerless to oppose him. The knight pushed her down roughly, forcing her neck onto the block. He stood with his foot in the middle of her back, to hold her in position. She flailed her arms helplessly.

She saw a shadow move across the grass as he raised his ax into the air.

The telephone rang insistently, loudly. David Stern yawned, flicked on the bedside lamp, picked up the receiver. "Hello," he said, his voice groggy.

"David, it's John Gordon. You'd better come down to the transit room."

Stern fumbled for his glasses, looked at his watch. It was 6:20 a.m. He had slept for three hours.

"There's a decision to make," Gordon said. "I'll be up to get you in five minutes."

"Okay," Stern said, and hung up. He got out of bed and opened the blinds at the window; bright sunlight shone in, so bright that it made him squint. He headed for the bathroom to take a shower.

He was in one of three rooms that ITC maintained in their laboratory building for researchers who had to work through the night. It was equipped like a hotel room, even down to the little bottles of shampoo and moisturizing cream by the sink. Stern shaved and dressed, then stepped out into the hallway. He didn't see Gordon anywhere, but he heard voices from the far end of the corridor. He walked down the hall, looking through the glass doors into the various labs. They were all deserted at this hour.

But at the end of the corridor, he found a lab with its door open. A workman with a yellow tape was measuring the height and width of the doorway. Inside, four technicians were all standing around a large table, looking down at it. On the table was a large scale model built of pale wood, showing the fortress of La Roque and the surrounding area. The men were murmuring to one another, and one was tentatively lifting the edge of the table. It seemed they were trying to figure out how to move it.

"Doniger says he has to have it," the technician said, "as an exhibit after the presentation."

"I don't see how we get it out of the room," another said. "How'd they get it in?"

"They built it in place."

"It'll just make it," said the man at the door, snapping his tape measure shut.

Curious, Stern walked into the room, looked more closely at the model. It showed the castle, recognizable and accurate, in the center of a much larger complex. Beyond the castle was a ring of foliage, and outside that a complex of blocky buildings and a network of roads. Yet none of that existed. In medieval times, the castle had stood alone on a plain.