Lightning

showed up in the time stream to warn us. So if they came back
before
he warned us—then how could he have warned us in the first place, and how could we be here where we are now, alive? Paradox!"
    He laughed and clapped his hands like a gnome chortling over some particularly amusing side-effect of a magical spell.
    In contrast to his good humor, Laura was getting a headache from trying to sort out the complexities of this thing.
    Chris said, "Some people believe time travel isn't even possible 'cause of all the paradoxes. But some believe it's possible so long as the trip you make into the past doesn't create a paradox. Now if
that's
true, see, then the killers couldn't come back on a second, earlier trip 'cause two of them had already been killed on
the first
trip. They couldn't do it because they were already dead, and it was a paradox. But the guys you didn't kill and maybe some
new
time travelers could make another trip to cut us off at the end of this road." He leaned forward to peer through the streaked windshield again. "That's what all that lightning was off to the south when we were weaving to keep them from shooting us—more guys from the future were arriving. Yeah, I'll bet they're waiting for us down there somewhere, down there in the dark."
    Rubbing her temples with her fingertips, Laura said, "But if we turn around and go back, if we don't drive into the trap ahead, then they'll realize we've outthought them. And so they'll make a
third
trip back in time and return to the Mercedes and shoot us when we try to drive back that way. They'll get us no matter which way we go."
    He shook his head vigorously. "No. Because by the time they realize we're on to them, maybe half an hour from now, we'll already have turned around and driven back past the Mercedes." The boy was bouncing up and down in his seat with excitement now. "So if they try to make a
third
trip in time to go back to the beginning of this road and trap us there, they can't do it, because we'll already have driven back that way and out, we'll already be safe. Paradox! See, they got to play by the rules, Mom. They're not magical. They got to play by the rules, and they can be beat!"
    In thirty-three years she had never had a headache that had gone from a mild throb to a pounding skull-splitter as quickly as this one. The more she tried to puzzle out the difficulties of avoiding a pack of time-traveling hitmen, the deeper rooted the pain became.
    Finally she said, "I give up. I guess I should've been watching
Star Trek
and reading Robert Heinlein all these years instead of being a serious adult, because I'm just not able to cope with this. So I'll tell you what: I'm going to rely on
you
to outsmart them. You'll have to try to keep one step ahead of them. They want us dead. So how can they try to kill us without creating one of these paradoxes? Where will they show up next… and next? Right now, we're going to go back the way we came, past the Mercedes, and if you're right, no one will be waiting there for us. So where will they show up after that? Will we see them again tonight? Think about those things, and when you have any ideas, let me know what they are."
    "I will, Mom." He slumped down in his seat, grinning broadly for a moment, then chewing on his lip as he settled deeper into the game.
    Except it was not a game, of course. Their lives were really at stake. They had to elude killers with nearly superhuman abilities, and they were pinning their hopes of survival on nothing more than the richness of an eight-year-old boy's imagination.
    Laura started the Jeep, put it in reverse, and backed up a couple of hundred yards until she found a place in the road wide enough to turn around. Then they headed back the way they had come, toward the Mercedes in the ditch, toward Big Bear.
    She was beyond terror. Their situation contained such a large element of the unknown—and unknowable—that terror could not be sustained. Terror was not like happiness or depression; it was an
acute
condition that by its very nature had to be of a short term. Terror wilted fast. Or it escalated until you passed out or until you died of it, frightened to death; you screamed until a blood vessel burst in your brain. She wasn't screaming, and in spite of her headache she didn't think any vessels were going to burst. She settled into a low-key, chronic fear, hardly more than anxiety.
    What a day this had been. What a year. What a life.
    Exotic news.
2
    They passed the