Theo urged the cart to go faster. He remembered the old golf carts CERN used to have for traveling short distances in the tunnel. He missed those; at least they weren't constantly in danger of flipping over at high speeds.

They continued on, farther and farther, swinging around the tunnel, and—

A great crashing sound from the rear. Theo looked back. Rusch's cart had smashed into the outside wall. It had come to a dead stop. Theo let out a small cheer.

He figured they'd gone about seventeen kilometers now — soon the staging area for the campus monorail station would be swinging into view. He might be able to get out there and take the elevator straight up into the LHC control center. He hoped he'd see the monorail parked back there, meaning Jake and Moot had made it to safety, and—

God damn it! His hovercart was dying, its battery exhausted. It had probably sounded an alarm earlier, but Theo had been unable to hear it over the noise the overtaxed engines were making. The cart dropped to the tunnel floor, skidding a distance along its concrete surface before coming to a dead halt. Theo grabbed the bomb and began to run. As a teenager, Theo had once participated in a re-creation of the run from Marathon to Athens made in 490 B.C. to announce a Hellenic victory over the Persians — but he'd been thirty years younger then. His heart was pounding now as he tried to go faster.

Kablam!

Another gunshot. Rusch must have gotten his cart going again. Theo kept running, his legs pounding, at least in his mind, like pistons. There, ahead, was the main campus staging area, a half dozen hovercarts parked along its wall. Only another twenty meters—

He glanced back. Rusch was closing rapidly. Christ, he couldn't stop here, either — Rusch would pick him off like a sitting duck.

Theo forced his body to make it the last few meters, and—

The chase continued.

He tumbled into another hovercart and sent himself careening once more down the tunnel, still heading clockwise. He looked back. Rusch dumped his own hovercart, presumably worried about its batteries, and transferred to a fresh one. He headed off in hot pursuit.

Theo glanced at the bomb's timer. Only twenty minutes left, but for once Theo seemed to have a decent lead. And, because of that, he actually stopped to think for a moment. Could Rusch possibly be right? Could there be a chance to undo all the damage, all the death that had occurred twenty-one years ago? If there had never been visions, Rusch's wife might still be alive; Michiko's daughter Tamiko might still be alive; Theo's brother Dimitrios might still be alive.

But, of course, no one conceived after the visions — no one born in the last twenty years — would be the same. Which sperm penetrated an egg was dependent on a thousand details; if the world unfolded differently, if women got pregnant on different days, or even different seconds, their children would be different. There were — what? — something like four billion people who had been born in the last two decades. Even if he could rewrite history, did he have any right to do so? Didn't those billions deserve the rest of their allotted three score and ten, rather than to be simply snuffed out, not even killed but completely expunged from the timeline?

Theo's cart continued its journey around the tunnel. He glanced back; Rusch was emerging in the distance from behind the curve.

No. No, he wouldn't change the past even if he could. And besides, he didn't really believe Rusch. Yes, the future could be changed. But the past? No, that had to be fixed. Upon that much he'd always agreed with Lloyd Simcoe. What this Rusch was saying was crazy.

Another gunshot! The bullet missed him, impacting the tunnel wall up ahead. But there would doubtless be more, if Rusch realized where Theo was headed—

Another kilometer slipped by. The bomb's timer now read just eleven minutes. Theo looked at the wall markings, trying to make them out in the dim light of his headlights. It had to be just ahead, and—

There it was! Just where he'd left it!

The monorail, hanging from the ceiling. If he could make it there—

A new shot rang out. This one did hit the hovercart, and Theo almost lost control of the vehicle again. The monorail was still a hundred meters ahead. Theo fought with the joystick again, swearing at the cart, demanding it go faster, faster—

The monorail had five components — a cab at each end, and three cars in the middle. He had to make it to the far cab; the train would only move in the direction it thought of as forward.

Almost there—

He didn't slow the hovercart gently; instead, he just slammed the brake. The vehicle pitched forward, Theo being tossed with it. It smashed onto the tunnel floor, skidding along, sparks flying. Theo got out, grabbing the bomb, and—

Yet another shot and—

God!

A shower of Theo's own blood splashing against his face—

More pain than he'd ever felt in his life—

A bullet tearing into his right shoulder.

God—

He dropped the bomb, scrambled for it again with his left hand, and staggered into the monorail's cab.

The pain — incredible pain—

He hit the monorail's start button.

Its headlights, mounted above the angled windscreen, snapped on, illuminating the tunnel ahead. After the dimness of the last half hour, the light was painfully bright.

The monorail heaved into motion, whining as it did so. Theo pushed the speed control; the train moved faster and faster still.

Theo thought he was going to black out from the pain. He looked back. Rusch was negotiating his cart past Theo's abandoned one. The monorail used magnetic levitation; it was capable of very high speeds. Of course, no one had ever tested its maximum velocity in the tunnel—

Until now.

The bomb's display said eight minutes.

Another bullet rang out, but it missed its mark. Theo glanced back just in time to see Rusch's cart fall back around the curve of the tunnel.

Theo leaned his head out the side of the cab; there was wind in his face. "Come on," he said. "Come on… "

The tunnel's curving walls flashed by. The mag-lev generators hummed loudly.

There they were: Jake and Moot, the physicist attending to the cop, who was now sitting up, mercifully alive. Theo waved at them as the monorail zoomed past.

Kilometers passed, and then—

Sixty seconds.

He'd never make it to the far access station, never make it to the surface. Maybe he should just drop the bomb; yes, it would disable the LHC no matter where it exploded, but—

No.

No, he had come too far — and he had no fatal flaw; his downfall was not preordained.

If only—

He looked at the timer again, then at the wall markings.

Yes!

Yes! He might just make it!

He urged the train to go even faster.

And then—

The tunnel straightened out.

He hit the emergency brake.

Another shower of sparks.

Metal against metal.

His head whipping forward—

Agony in his shoulder—

He clambered out of the cramped cab and staggered away from the monorail.

Forty-five seconds—

Staggered a few meters farther along the tunnel—

To the entrance to the huge, empty, six-story-tall chamber that had once housed the CMS detector.

He forced himself to go on, into the chamber, placing the bomb in the center of the vast empty space.

Thirty seconds.

He turned around, ran as fast as he could, appalled to see the river of blood he'd left on his way in—

Back out to the monorail—

Fifteen seconds.

Clambering back into the cab, hitting the accelerator—

Ten seconds.

Zipping along the roof-mounted track—

Five seconds.

Around the curve of the tunnel—

Four seconds.

Almost unconscious from the pain—