“Yes, yes, that’s hard to keep in mind, forgive me.” Bill looked out the window again, marveling at what seemed to Leyster a perfectly ordinary tract of row houses. “I can’t believe how much has changed in only ten years. So very many things are going to happen in the next decade!”

“Anything important?”

“Compared to this? Compared to time travel? Nothing. Nothing at all.”

The marine guard who, they’d been told, had orders to shoot anyone who tried to leave the van before being told to, and to whom they had also been directed to say nothing of their origins or destination, looked uncomfortable.

Orientation was held in the Crystal Gateway Marriott. It was easily the strangest conference Leyster had ever attended.

In some ways it was the best. One advantage of time travel was that the Proceedings could be made available at the beginning of the conference. It still took a year or more for the papers to be assembled, edited, and printed, but the books themselves could then be shipped back and sold at the registration table, so they could be carried from talk to talk, and annotated as the papers were presented.

On the negative side, Leyster recognized only a fraction of those present. Paleontology was a small world—there were only two or three thousand professionals in existence at any given moment. Most conferences, he knew everyone of importance, and was at least vaguely familiar with the faces of the rest. Here, though, with professionals recruited across the span of twenty-some years, there were many who were strange to him. Even those he thought he knew had aged and changed to the point where he didn’t feel comfortable approaching them. He was no longer certain who anybody was.

He snagged a bear claw from the buffet, and joined the line for coffee. Bill and Cedella got in line behind him, Bill with a slap on his shoulder, and Cedella with a bright flash of teeth. He was grateful for their company.

Cedella made a face when she took her first sip of coffee. “This stuff is as bad as ever. If we can put a man on the moon and travel a hundred million years into the past, why can’t we make a decent cup of coffee?”

“If you think that’s bad, you should try the decaf.”

“How this man suffers.” She turned to Leyster. “Do you see how he suffers?”

“I’ve been thinking about my book. It’s almost done, only I’m stuck on a title. I was thinking maybe Tracks of Time—”

“Oh, but that’s not the—”

Bill cleared his throat, and Cedella fell silent. “We’re really not supposed to say,” he said gently. “I do apologize, but they were quite firm on that score.”

“Come! The morning keynote speech starts in a few minutes. I want to get a good seat.”

Leyster trailed after them into the Grand Ballroom. There was a happy buzz of anticipation in the room. Everyone was anxious to get things started. When the conference was over, they’d begin preparations for their first field trips back into deep time, to encounter in the flesh what they now knew only from impressions in stone. They were like so many fledglings nervously standing on their cliff face ledge, knowing that soon they would step over the edge, spread wings, and fly.

The seats filled up. Somebody dimmed the lights.

Griffin took the podium. He looked much older than Leyster recalled him being.

“First slide, please.”

The slide showed the cartoon caveman Alley Oop, caressing the head of his faithful dinosaur mount, Dinny. There was light laughter.

“In just a moment we’ll get to what I believe is technically known as ‘the good stuff.’ And what we have is spectacular. In addition to the papers, there will be a film program tonight—actual footage of live dinosaurs from the Triassic, Jurassic, and Cretaceous. The film has been chosen by your fellow vertebrate paleontologists from generation two, and they’ve taken care that all your favorites will be there. I can guarantee you—there will be surprises.”

Several in the audience applauded.

“However, before we can proceed, I am required to share with you a few of the rules of the road. Everyone here has already been told the penalties for violating secrecy. Today I’m going to explain why those penalties are so Draconian. Now, our physicists have requested that I share with you as little of the mechanics of time travel as possible. Slide?”

The new slide showed a dense throng of mathematical notations. Leyster assumed they were not taken from the actual equations of time travel, but they could have been no more incomprehensible if they had been.

“No problem.”

Laughter.

“In order to hold such conferences as this one, we will be shuttling researchers back and forth across a period of the next century or so. It’s bound to occur to a few of you that there’s a wealth of information to be gleaned from a copy of next year’s newspaper. Lottery numbers. World Cup winners. Stock prices. What’s to keep you from jotting down a few numbers and taking advantage of them? Only one thing:

“Paradox.

“A paradox is anything self-contradictory and yet irreconcilable. For example, the barber of Seville, who shaves everyone in town who doesn’t shave himself. Does he shave himself or not? The statement, ‘This sentence is a lie.’ True or false? A little closer to the bone, a man goes into the past and kills his grandfather as a child, thus preventing his own birth. How can he exist, then, to commit the murder in the first place?

“Without time travel, paradoxes are pleasant logical puzzles which can be neatly dispatched with a tweak in the rules of logic dealing with self-reference. However, once it’s possible to physically invade the childhood of one’s grandparents, the resolution of paradoxes becomes vitally important. So we’ve given this some serious thought.”

Griffin paused, frowning down at his notes for a beat. Nobody made a sound. Leyster did not feel any particular warmth or charisma from the man, but he was clearly alone in this. The entire room was with Griffin.

“It turns out that paradox is deeply embedded in the nature of existence. The two are profoundly interrelated.

“Third slide.” Another cartoon, this one of an athletic man in Greek skirt and lace-up sandals running furiously toward a turtle crawling away from him on the road ahead.

“Consider Zeno’s first paradox. Achilles, the fastest man in the world, wishes to overtake a tortoise on the road ahead of him. He races toward it as swiftly as he can. However, by the time he reaches where the tortoise was, the tortoise is no longer there. It has moved a little further down the road. No problem. He simply races to that new spot. However, when he arrives there, he finds again that the tortoise has moved away. No matter how many times he tries, he can never catch up with the tortoise.”

Griffin produced a tennis ball from the pocket of his jacket. He tossed it lightly into the air, caught it on the way down. “Consider also, Zeno’s third paradox. Achilles draws his bow and shoots an arrow at a tree. The tree is not far distant. But in order for the arrow to reach the tree, it must first travel half the distance from the bow to the tree. In order to reach that midway point, it must travel half of that distance. And so on. In order to arrive anywhere, the arrow must perform an infinite number of operations. Which will take it an infinite amount of time. Obviously, it can never move.”

Suddenly he threw the ball as hard as he could. With a soft boom, it hit the closed ballroom doors and bounced away, up the aisle.

“Nevertheless—it moves. Paradox can and does happen. This is the riddle of Achilles. How can the seemingly self-contradictory exist so easily in this world?

“And to this riddle we have no answer.

“Now, in just a minute, I’m going to leave the room, and take a limo back to the Pentagon. The trip takes roughly half an hour. I’ll travel an hour into the past—so that I’ll emerge from the Pentagon exactly one half hour ago. A car will be waiting for me. I’ll ride it back here to the Marriott. The driver will let me off at the front door. I’ll walk through the lobby, down the hall, and to the closed doors of the Grand Ballroom.”