“Then… what are they?”

“If you ever need to know, you’ll be told. The operant fact is that the technology is on loan. As is ever the case with such gifts, there are a few strings. One of which is that we’re not allowed to meddle with causality.”

“Why?” Molly asked.

“I don’t know. The physicists—some of them—tell me that if even one observed event were undone, all of time and existence would start to unravel. Not just the future, but the past as well, so that we’d be destabilizing all of existence, from alpha to omega, the Big Bang to the Cold Dark. Other physicists tell me no such thing, of course. The truth? The truth is that the Unchanging don’t want us to do it.

“They’ve told us that if we ever violate their directives, they’ll go back to the instant before giving us time travel, and withhold the offer. Think about that! Everything we’ve done and labored for these many years will come to nothing. Our lives, our experiences will dissolve into timelike loops and futility. The project will have never been.

“Now. You’ve met these people—the paleontologists. If you told them that the price of time travel was five deaths, what would they say? Would they think the price was too high?”

His face grew uncertain in her eyes. She squeezed them tight shut for the briefest instant. When she opened them again, she felt compelled to stand and turn away from him. On the wall was a photograph. It had been taken at the opening of the dinosaur compound in the National Zoo, and showed Griffin and the then-Speaker of the House stagily pulling opposite ends of a T. rex wishbone. She stared at their stiff poses, their insincere grins.

“I won’t be a part of it. You cannot make me responsible for those deaths.”

“You already are.”

She shook her head. “What?”

“You remember that week you spent at Survival Station? Tom told you to make sure that Robo Boy heard that Leyster and Salley would be leading the first Baseline expedition. Tom got his directions from Jimmy, who was acting in response to a memo that Griffin should be writing up right now. You’ve already played your part.”

The Old Man spread his hands. “Can you go back and undo everything you did and said back then? Well, no more can I undo these five deaths.”

“I’ll quit anyway! I won’t be used like this!”

“Then twenty people die.” Griffin smiled sadly and spread his hands. “This is not a threat. Later in life, you’ll happen to be the right person in the right place at the right time. Resign now, and you won’t be there. Twenty people will die. Because you quit.”

Molly squeezed her eyes tight, against her tears. “You are an evil, evil man,” she said.

He made a warm, ambiguous sound that might have been a chuckle. “I know, dear. Believe me, I know.”

Lost Expedition Foothills: Mesozoic era. Cretaceous period. Senonian epoch. Maastrichtian age. 65 My B.CE.

They buried Lydia Pell on a fern-covered knoll above Hell Creek. There was some argument over what religion she was, because she had once jokingly referred to herself as a “heretic Taoist.” But then Katie went through her effects and found a pocket New Testament and a pendant cross made from three square-cut carpenter’s nails, and that pretty well settled it that she was a Christian.

While those who had kept the night watch over her corpse slept, Leyster spent the morning searching Gillian’s Bible for an appropriate passage. He’d considered “There were giants in the Earth,” or the verse about Leviathan. But such attempts to fit in a reference to dinosaurs made him feel as if he were cheapening the grandeur and meaning of Lydia Pell’s life by reducing it to the circumstances of her death. So in the end he settled for the Twenty-Third Psalm.

“The Lord is my shepherd,” he began. “I shall not want.” There were no sheep anywhere in the world, nor would there be for many tens of millions of years. Yet still, the words seemed appropriate. There was comfort in them.

The day was wet and miserable, but the rain was light and did not interfere with the ceremony. For most of the afternoon, everybody glumly carried stones from the creek to raise a small cairn over her grave, in order to keep scavengers away from her body. Just as they finished, the sun came out again.

Lai-tsz raised her head. “Listen,” she said. “Do you hear that?”

A distant murmurous sound rose up from the far side of the river. It sounded a little like geese honking.

All in a group they hurried up to the top of the hollow, where a gap in the trees afforded a partial view of the valley. There they saw that the land beyond the River Styx was in motion. Tamara scrambled up a tree and shouted down, “The herds are flooding in! They’re coming from all directions. More from the west than the east, though. I see hadrosaurs of some sort, and triceratopses too.”

“I didn’t bring my cameras!” wailed Patrick.

Tamara called down from the top of the tree, “Now they’re crossing the river! Holy cow. It’s incredible. They’re putting up so much mist you can’t see the half of them.”

Several others went swarming up the trees to see for themselves.

“Can you give us an estimate of their numbers?” Leyster shouted up.

“No way! I keep losing sight of them among the trees. Or in the water. But there must be hundreds of them. Maybe thousands.”

“Hundreds of hadrosaurs, or hundreds of triceratopses?”

“Both!”

“What are they doing on this side?”

“It’s hard to tell. Milling about, mostly. Some of the hadrosaurs appear to be breaking into smaller groups. The triceratopses are clustering.”

“So what do you think—are these guys migrating?”

“Actually, it looks like they’re moving in to stay.”

“They couldn’t have chosen a better time for it,” Katie commented. “All this young growth, freshly fertilized with titanosaur dung—it’s herbivore heaven here.”

“Damn.” Leyster thought for a moment, then said, “I want to go down by the river and get a closer look at them.” He was understating the case drastically. He had to go take a closer look. “Who here wants to go with me?”

Tamara swung down out of her tree so fast Leyster worried she would fall, singing, “Me! Me! Me!”

“Some of us should stay here,” Jamal said dubiously. “To look after the camp. Also we’ve still got the walls to put up.”

“Come with us,” Leyster said quietly. “Nobody can say you haven’t done your share of the work.”

Jamal hesitated, then shook his head. “No, really. How can I expect anybody else to work, if I’m not willing to work myself?”

The party he put together was, to Leyster’s profound disappointment, made up mostly of the food-gatherers and Daljit. Of the house-builders, only Patrick, loaded down with his cameras, broke ranks.

They moved cautiously, single file, like a jungle combat squad out of the twentieth century. Lai-tsz went first, toting one of the expedition’s four shotguns. Leyster doubted it would do much good in a confrontation with a full-sized dinosaur, but the idea was that the noise would frighten a predator away.

He sincerely hoped that was true.

They were deep into the valley flatlands before they spotted their first dinos—a clutch of hadrosaurs delicately grazing on the tender young shoots that grew thickly along the verges of the creek.

As one, all binoculars went up.

The animals paid them no attention. Every now and then one would bob up on its two hind feet and look around warily, then dip back down again. Briefly, the startling orange markings on either side of its head would erupt into the air like a burst of flame, before disappearing again into the new growth. There was always at least one keeping watch.