Close to Critical by Hal Clement

I should imagine; but he certainly' won't be easier to get away from." "Then maybe I shouldn't have come, Teacher. I'm sorry."
    "I'm not. My original plan for getting in touch with you again has already failed, so if you hadn't come we'd be in even worse shape. All I meant was that we have some heavy planning to do before we're out of this mess. You'd probably better get away for a few hours at least, while I think; there's no point in having you caught by Swift, too."
    "But how will I get back again? They have fire, now - for that matter, as soon as they come back they'll know I've been here, and probably start tracking me. I'd probably still be in sight, even if I started now; it's beginning to rain, and I can't travel without a torch, and that will be visible for miles. I was expecting you to come with me right away."
    "I see your trouble, but don't quite know what to do about it. It's hard to believe that Swift won't be back here in the next few minutes." Fagin paused, as though in thought; Nick of course did not know that such pauses really meant a tense conference among several men a hundred and sixty thousand miles away. "Look, Nick. There's a good deal of burnable material around, right?"
    "Yes."
    "And there is only one path from the cliff top, and that a narrow cleft?"
    "Yes, not counting the way around - a good four miles."
    "Hmph. I could wish it were longer. Do you think you can build a fire big enough to block the foot of that path for a while, so as to delay them while we get going? You'll have to work fast; they must be coming back by now, I should think, unless they're still looking for you on top."
    "I'll"try." Nick could see that this was no time for theorizing. "Someone's probably looked over the edge and seen me by now, but there's nothing to lose. If I don't catch up to you, head east-northeast until you reach the sea, then follow along its daytime shoreline until you meet the others. I'll do what I can to interfere with Swift's trackers; you'd better get going now."
    Nick didn't wait for a reply; he was already racing toward the foot of the cliff trail, gathering fuel as he went. His torch was nearly gone, but he started a rough heap of wood a few yards inside the cleft, and managed to get it burning. Then he hunted around madly, tossing every bit of combustible matter he could find into the four-yard-wide crack.
    A raindrop came squeezing its way down the gully and vanished as it neared the fire, but it was early enough in the evening for there still to be a good deal of oxygen in it. Nick was pleased; evidently no torch-bearing cave dwellers were yet on the path, or the drop would have been destroyed much sooner. That gave so much more time.
    With the pile big enough to satisfy him, he set off along Fagin's trail. Even Nick could follow it, a fivefoot-wide track of flattened and crumbled vegetation, except where it led through hollows already filling with liquid water. He could have gone through these with his torch, since the liquid was still fairly safe to breathe, but he chose to detour around. Even so, he caught up with Fagin within a mile.
    "Keep going," he said. "I'm going to do a little trail erasing." He applied his torch to a bush beside the trail, and to the crushed, brittle material on the track itself; then he started in a wide arc to the north, setting fire to every bush he passed. Eventually, a glowing belt of radiance extended from Fagin's trail almost east of the cave village around to the track down which the robot had been brought from the north. Nick thought he could hear excited voices from the caves, but wasn't sure. He raced northward at the top of his speed for another mile, and started another series of fires there. They should be visible from the cliff, too; and perhaps the cave dwellers would come out and search along the route to the old village rather than start tracking right away. Then he raced back to intercept Fagin's trail, shielding his torch with his body in the hope