What time had he spoken with his father on that night? On this this night? night?

He couldn't remember. He'd been watching the TV but wasn't sure what had been on. Okay. It was simple enough. The time at the moment was eleven minutes after nine. He set the Q-pod to take him forward to ten o'clock.

The darkness faded and came back. And he realized he was standing in the middle of the driveway. Time traveler run down by father.

But no car was coming, and the garage was still empty. He was sure the call hadn't come in after eleven, so he set the device to move forward one hour. This time he walked onto the lawn before activating.

And the black Skylark had arrived. Inside the house, lights were on.

Who said Shel wasn't brilliant? He congratulated himself and knocked at the front door. There was movement inside, the living-room lights came on, and the door opened.

His father's eyes went wide. "Adrian."

"Hi, Dad." They stood for a long moment staring at each other. "Did you want to invite me in?"

"Yes. Of course." He stepped back. "I just got finished talking to you."

"I know."

Michael Shelborne resembled Jerry more than he did Shel. Or would have had Jerry not picked up weight. His father was tall, lean, with thick black hair and the kind of face that would have allowed him to play Sher lock Holmes. "Adrian, were you in your car when we talked?"

"No."

"I thought not."

Shel showed him the Q-pod. His father acquired a distinctly unhappy expression. "Come in," he said, using a tone that one might adopt to a sixteen-year-old caught smuggling his girlfriend into the house.

They sat down while the elder Shelborne contented himself with glaring at one of the walls. Then the eyes, dark, penetrating, cool even when he was irritated, locked on him.

"Where are you going, Dad?" Shel asked innocently.

"Why does it matter?"

"That lunch tomorrow?" Shel made no effort to hide an accusing tone. "You never showed up. Or, rather, you won't won't show up." show up."

"What happened?"

"That's what I wanted to ask you."

He'd settled into an armchair. Now he pushed back in it, licked his lips, and braced his jaw on one fist. "Is that why you're here?"

"Isn't it sufficient reason?"

"Don't tell me any more," he said.

"Why not?"

"Trust me." He indicated the Q-pod, which Shel had attached to his belt. "How long have you known about that?"

"A couple of days. To be honest, it's hard to be sure. What day is this?"

"Monday."

"Incredible. A few minutes ago it was Thursday."

Michael's eyes closed. "Look, Adrian, I know you're probably upset."

"Did you make this thing?"

"You were supposed to destroy it."

"I'm glad I didn't."

"I'm sure you are." Michael pressed his lips together. "Yes, I made it. Along with a colleague."

"Why do you want it destroyed?"

"Because it's dangerous."

"Why's that?"

"For a number of reasons."

"Tell me about them. I don't have a clue what's going on."

"I take it I haven't turned up since the lunch?"

"No. You've been missing nine days."

"Okay."

"Where were you planning to go?"

He laughed. "You wouldn't believe it."

"At this point, I'm ready to believe anything anything."

He smiled, casually, easily, like a man in charge of the world. "You know what the converters can do."

"A converter. Is that what you call it?"

"Yes. But the name's not important."

"I guess not. So where did you go? Where are you going?"

"I'd always wanted to spend some time with Galileo."

"Galileo."

"Or maybe Cicero. Or Ben Franklin." He managed a smile. "I haven't made up my mind yet."

"You've had this thing-what?-three or four months? It's part of that government project, right?"

"More or less."

"How do you mean, 'more or less'?"

"It was an accidental discovery. We were working on something else."

"Okay. So now the government has time-travel capability."

"No."

"No? Why not?"

"It's too dangerous to put in anybody's hands. Let alone a government."

"You keep saying it's dangerous."

"I don't think we would be permitted to change the past. Though there are people who'd want to. h.e.l.l, I'd I'd want to. You could save Lincoln. Kill Hitler. Things like that. But I'm not certain what the result would be." want to. You could save Lincoln. Kill Hitler. Things like that. But I'm not certain what the result would be."

"I'm not sure I'm following."

"We had reason to believe that the time stream has a lot of flexibility. You can go back and do things, and the continuum will adjust. As long as you don't create a paradox. A loop. Something that can't be absorbed."

"What makes you say that?"

"The math suggests it. But we pushed it too far. We did an experiment."

"I'm listening."

"Adrian, my partner in the research was Ivy Kla.s.sen."

"Was?"

"She's dead."

"What happened?"

"The experiment."

"Explain."

"What happens if someone goes back and rescues JFK? Prevents his going to Dallas?"

"I don't know. We stay out of Vietnam?"

"I don't know either. What we do do know is that it didn't happen. Look, Adrian, the standard theory is that if you go back and rescue Kennedy, you cause a split in the timeline. Another reality is created. That's nonsense, of course, but if it happened, there'd be diverging timelines. The one we live in, and the one in which he survives." know is that it didn't happen. Look, Adrian, the standard theory is that if you go back and rescue Kennedy, you cause a split in the timeline. Another reality is created. That's nonsense, of course, but if it happened, there'd be diverging timelines. The one we live in, and the one in which he survives."

"And that's what you wanted to test?"

"Yes."

"What did you try to do? Post somebody at the Texas School Book Depository?"

"We did a different kind of test. We put a copy of a book into a briefcase."

"Why are you laughing?"

"Because of the book. Anyhow, we closed the briefcase. Left it alone in Ivy's office for fifteen minutes. Then we went in and opened it. The book was still there."

"I would think so."

"Then Ivy used the converter to go back five minutes, to a time before we looked in the briefcase. The intention was that she'd remove the book."

"So it should have been empty when you opened it."

"Yes. But had it been empty when we opened it, then Ivy would have done nothing. Either way, we'd have had a paradox. We would have changed reality."

"So what happened?"

"I found her dead in the office."

"What? How?"

"The doctors said it was a heart attack."

"My G.o.d."

"She was twenty-seven. In perfect health, as far as anyone knew." He sighed. "It was my fault, Adrian."

"Why do you say that?"

"I should have realized there might be a factor, something built into the continuum that prevents our s.c.r.e.w.i.n.g around with it. No paradox allowed."

"But we've both traveled in time. I did it tonight. This was a conversation that did not take place. And here we are."

"How can you say it didn't take place? It is is taking place. I did not live through a variant of this evening in which I called you, agreed to meet you and Jerry at Servio's, and you taking place. I did not live through a variant of this evening in which I called you, agreed to meet you and Jerry at Servio's, and you didn't didn't show up here with a converter. show up here with a converter.

"Listen, son, if we went back to watch the signing of the Magna Carta, then we were were part of the event. If photographers had been there, taking pictures, they would have gotten us, as well as the other witnesses. There never would have been a Magna Carta event that we did not attend. I think-I can't be sure, but I part of the event. If photographers had been there, taking pictures, they would have gotten us, as well as the other witnesses. There never would have been a Magna Carta event that we did not attend. I think-I can't be sure, but I think think-it's only when we violate the time flow, when we create a situation we know could not have existed, that a corrective sets in."

"A corrective."

"Call it a principle that maintains chronological integrity. That prevents modifications to history. It disallows paradoxes. Negates contradictions."

"A chronological integrity principle."

"Yes."