Below, the boy leapt into the air, gripped the branch, and pulled quickly up. Although slim, he was surprisingly strong, and he moved from branch to branch surely. Chris was now about twenty feet above the ground. His arms burned, he was gasping as he went up, but he kept on going, branch to branch.

The boy gripped his calf, and he froze. Slowly, cautiously, he looked back over his shoulder, and saw the boy rigid on the branch beneath him. Then Chris heard the soft snort of a horse and realized the sound was close.

Very close.

On the ground below, six riders moved slowly and silently forward. They were still some distance away, intermittently visible through gaps in the foliage. When a horse snorted, its rider leaned forward to pat its neck to quiet it.

The riders knew they were close to their prey. They leaned over in their saddles, scanning the ground, looking to one side and the other. Fortunately they were now among the scrubby low pines; no trail was visible.

Communicating by hand gestures, they moved apart, separating themselves as they came forward. Now they formed a rough line, passing beneath the tree on both sides. Chris held his breath. If they looked up…

But they didn't.

They moved onward, deeper into the forest, and finally one of them spoke aloud. It was the rider with the black plume on his helmet, the one who had cut off Gomez's head. His visor was up.

"Here is enough. They have slipped us."

"How? Over the cliff?"

The black knight shook his head. "The child is not so foolish." Chris saw his face was dark: dark complexion and dark eyes.

"Nor quite a child, my Lord."

"If he fell, it was by error. It could not be otherwise. But I think we have gone awry. Let us return as we came."

"My Lord."

The riders turned their mounts and started back. They passed beneath the tree again, and then rode off, still widely spaced, heading into sunlight.

"Perhaps in better light, we shall find their track."

Chris gave a long sigh of relief.

The boy below tapped him on the leg and nodded to him, as if to say, Good work. They waited until the riders were at least a hundred yards away, nearly out of sight. Then the boy slipped quietly down the tree, and Chris followed as best he could.

Once on the ground, Chris saw the riders moving off. They were coming to the tree with the muddy footprints. The black knight passed it, not noticing. Then the next-

The boy grabbed his arm, pulled him away, slipping off in the underbrush.

Then: "Sir Guy! Look you here! The tree! They are in the tree!"

One of the knights had noticed.

Shit.

The riders spun on their mounts, looking up at the tree. The black knight came back, skeptical. "Eh? Show me."

"I do not see them up there, my Lord."

The knights turned, looked back, looked in all directions, looked behind them…

And they saw them.

"There!"

The riders charged.

The boy ran hard. "God's truth, we are lost now," he said, glancing over his shoulder as he raced forward. "Can you swim?"

"Swim?" Chris said.

Of course he could swim. But that was not what he was thinking about. Because right now they were running hard, flat out - toward the clearing, toward the break in the trees.

Toward the cliff.

The land sloped downward, gently at first, then more steeply. The ground cover became thinner, with exposed patches of yellow-white limestone. The sunlight was glaring.

The black knight bellowed something. Chris didn't understand it.

They came at last to the edge of the clearing. Without hesitation, the boy leapt into space.

Chris hesitated, not wanting to follow. Glancing back, he saw the knights charging him, their broadswords raised.

No choice.

Chris turned and ran forward toward the cliff edge.

Marek winced as he heard Chris's scream in his earpiece. The scream was loud at first, then abruptly ended with a grunt and a crashing sound.

An impact.

He stood with Kate by the trail, listening. Waiting.

They heard nothing more. Not even the crackle of static.

Nothing at all.

"Is he dead?" Kate said.

Marek didn't answer her. He walked quickly to Gomez's body, crouched down, and started searching in the mud. "Come on," he said. "Help me find that spare marker."

They searched for the next few minutes, and then Marek grabbed Gomez's hand, already turning pale gray, the muscles stiffening. He lifted her arm, feeling the coldness of her skin, and turned her torso over. The body splashed back in the mud.

That was when he noticed that Gomez had a bracelet of braided twine on her wrist. Marek hadn't noticed it before; it seemed to be part of her period costume. Of course, it was completely wrong for the period. Even a modest peasant woman would wear a bracelet of metal, or carved stone or wood, if she wore anything at all. This was a hippie-dippy modern thing.

Marek touched it curiously, and he was surprised to find it was stiff, almost like cardboard. He turned it on her wrist, looking for the latch, and a sort of lid flicked open in the braided twine, and he realized that the bracelet covered a small electronic timer, like a wristwatch.

The timer read: 36:10:37.

And it was counting backward.

He knew at once what it was. It was an elapsed counter for the machine, showing how much time they had left. They had thirty-seven hours initially, and now they had lost about fifty minutes.

We should hold on to this, he thought. He untied the bracelet from her arm, then wrapped it around his own wrist. He flipped the little lid shut.

"We've got a timer," Kate said. "But no marker."

They searched for the next five minutes. And finally, reluctantly, Marek had to admit the hard truth.

There was no marker. And without a marker, the machines would not come back.

Chris was right: they were trapped there.

In the control room, an alarm rang insistently. The technicians both got up from their consoles and started out of the room. Stern felt Gordon grab him firmly by the arm.

"We have to go," Gordon said. "The air's contaminated from the hydrofluoric acid. The transit pad is toxic. And the fumes will be up here, too, soon enough." He began to lead Stern out of the control room.

Stern glanced back at the screen, at the jumble of girders in smoke in the transit site. "But what if they try to come back when everybody is gone?"

"Don't worry," Gordon said. "That can't happen. The wreckage will trigger the infrared. The sensors need six feet on all sides, remember? Two meters. They don't have it. So the sensors won't let the machines come back. Not until we get all that cleared away."

"How long will it take to clear it away?"

"First, we have to exchange the air in the cave."

Gordon took Stern back to the long corridor leading to the main elevator. There were a lot of people in the corridor, all leaving. Their voices echoed in the tunnel.

"Exchange the air in the cave?" Stern said. "That's a huge volume. How long will that take?"

Gordon said, "In theory, it takes nine hours."

"In theory?"

"We've never had to do it before," Gordon said. "But we have the capacity, of course. The big fans should cut in any minute."

A few seconds later, a roaring sound filled the tunnel. Stern felt a blast of wind press his body, tug at his clothes.

"And after they exchange all the air? What then?"

"We rebuild the transit pad and wait for them to come back," Gordon said. "Just the way we were planning to do."

"And if they try to come back before you're ready for them?"

"It's not a problem, David. The machine will just refuse. It'll pop them right back to where they were. For the time being."