Powell whispered, "Think it sensed us?"
"Hope not. But we'd better flank them. Take the first side tunnel to the right."
"Suppose we miss them altogether?"
"Well what do you want to do? Go back?" Donovan grunted fiercely. "They're within a quarter of a mile. I was watching them through the visiplate, wasn't I? And we've got two days-"
"Oh, shut up. You're wasting your oxygen. Is this a side passage here?" The flash flicked. "It is. Let's go."
The vibration was considerably more marked and the ground below shuddered uneasily.
"This is good," said Donovan, "if it doesn't give out on us, though." He flung his light ahead anxiously.
They could touch the roof of the tunnel with a halfupstretched hand, and the bracings had been newly placed.
Donovan hesitated, "Dead end, let's go back."
"No. Hold on." Powell squeezed clumsily past. "Is that light ahead?"
"Light? I don't see any. Where would there be light down here?"
"Robot light." He was scrambling up a gentle incline on hands and knees. His voice was hoarse and anxious in Donovan's ears. "Hey, Mike, come up here."
There was light. Donovan crawled up and over Powell's outstretched legs. "An opening?"
"Yes. They must be working into this tunnel from the other side now I think."
Donovan felt the ragged edges of the opening that looked out into what the cautious flashlight showed to be a larger and obviously mainstem tunnel. The hole was too small for a man to go through, almost too small for two men to look through simultaneously.
There's nothing there," said Donovan.
"Well, not now. But there must have been a second ago or we wouldn't have seen light. Watch out!"
The walls rolled about them and they felt the impact. A fine dust showered down. Powell lifted a cautious head and looked again. "All right, Mike. They're there."
The glittering robots clustered fifty feet down the main stem. Metal arms labored mightily at the rubbish heap brought down by the last blast.
Donovan urged eagerly, "Don't waste time. It won't be long before they get through, and the next blast may get us."
"For Pete's sake, don't rush me." Powell unlimbered the detonator, and his eyes searched anxiously across the dusky background where the only light was robot light and it was impossible to tell a projecting boulder from a shadow.
"There's a spot in the roof, see it, almost over them. The last blast didn't quite get it. If you can get it at the base, half the roof will cave in."
Powell followed the dim finger, "Check! Now fasten your eye on the robots and pray they don't move too far from that part of the tunnel. They're my light sources. Are all seven there?"
Donovan counted, "All seven."
"Well, then, watch them. Watch every motion!"
His detonator was lifted and remained poised while Donovan watched and cursed and blinked the sweat out of his eye.
It flashed!
There was a jar, a series of hard vibrations, and then a jarring thump that threw Powell heavily against Donovan.
Donovan yowled, "Greg, you threw me off. I didn't see a thing."
Powell stared about wildly, "Where are they?"
Donovan fell into a stupid silence. There was no sign of the robots. It was dark as the depths of the River Styx.
"Think we buried them?" quavered Donovan.
"Let's get down there. Don't ask me what I think." Powell crawled backward at tumbling speed.
"Mike!"
Donovan paused in the act of following. "What's wrong now?"
"Hold on!" Powell's breathing was rough and irregular in Donovan's ears. "Mike! Do you hear me, Mike?"
"I'm right here. What is it?"
"We're blocked in. It wasn't the ceiling coming down fifty feet away that knocked us over. It was our own ceiling. The shock's tumbled it!"
"What!" Donovan scrambled up against a hard barrier. "Turn on the flash."
Powell did so. At no point was there room for a rabbit to squeeze through.
Donovan said softly, "Well, what do you know?"
They wasted a few moments and some muscular power in an effort to move the blocking barrier. Powell varied this by wrenching at the edges of the original hole. For a moment, Powell lifted his blaster. But in those close quarters, a flash would be suicide and he knew it. He sat down.
"You know, Mike," he said, "we've really messed this up. We are no nearer finding out what's wrong with Dave. It was a good idea but it blew up in our face."
Donovan's glance was bitter with an intensity totally wasted on the darkness, "I hate to disturb you, old man, but quite apart from what we know or don't know of Dave, we're slightly trapped. If we don't get loose, fella, we're going to die. D-I-E, die. How much oxygen have we anyway? Not more than six hours."
"I've thought of that." Powell's fingers went up to his long-suffering mustache and clanged uselessly against the transparent visor. "Of course, we could get Dave to dig us out easily in that time, except that our precious emergency must have thrown him off, and his radio circuit is out."
"And isn't that nice?"
Donovan edged up to the opening and managed to get his metalincased head out. It was an extremely tight fit.
"Hey, Greg!"
"What?"
"Suppose we get Dave within twenty feet. He'll snap to normal. That will save us."
"Sure, but where is he?"
"Down the corridor - way down. For Pete's sake, stop pulling before you drag my head out of its socket. I'll give you your chance to look."