The Paradox of the Sets

by Brian Stableford

  When we’d rested for the best part of an hour, I felt fit enough to go on. By that time Gley was already a little bit impatient.

  This time it was a little easier in that the slant of the tunnel was more gentle. But the tunnel was more nearly circular in section, and this meant that we were often reduced to crawling like worms. Getting through the narrow passages was like trying to force corks through bottlenecks.

  We were no longer in a simple shaft—here the walls were frequently cracked and faulted, and the gas coming up through some of the cracks was warm. The walls were wet with a greasy dampness that gave me the uncomfortable feeling that the walls were suppurating. I didn’t like the way that some of the stickiness came off on to my suit, lubricating it. I could keep the gauntlets and my helmet free of the stuff, but I worried about the boots and the footholds they might slip out of. Had the way been as steep as it had previously I would have wanted to call the whole thing off, but it was unpleasant rather than actually dangerous.

  I kept glancing at my watch occasionally to note the passage of time since the resting place, but it was still registering ship-standard time, and though it didn’t matter a damn down here how long the hours and minutes were by comparison to the planetary day I still had the feeling that the hour indicated was unreal and lacking in meaning.

  Inevitably, I began to have second thoughts about the wisdom of all this. If there had been an underground installation it was obviously way above us by now. There had been no sign whatever of human or alien agency in the bubble-cave where we’d stopped. If there were signs that the crater area had once been inhabited in a lower cave-system then nothing significant had descended by the way we were coming. Except perhaps a mysterious predator—a monster from some mysterious underworld. We seemed to be miles below the surface now, though my watch assured me that was nonsense. It seemed like an age since I had last seen the light, but it was only a matter of hours, and though we seemed to have moved quickly we had been making our way in a painstaking fashion. It was easy here to fall prey to the illusion that we had entered another world remote from the one we had left, and that there could be no connection between this wet wormhole curling its way claustrophobically through the mountain and the world of trees and multicolored blossoms beneath the infinite sky, but illusion it was. We were still within the planet’s outermost shell, nor could we ever hope to penetrate it.

  Eventually, after nearly getting stuck and being forced back, we found another section that was almost level, where we could comfortably sit and rest. The tunnel had veered away to one side by now, and we were hardly getting deeper at all. The walls were uniform, almost polished. Their basic color was gray but they were streaked here and there with white and sometimes with green.

  “This was never a blow-hole,” observed Gley. “This rock’s never been molten. The only thing that’s ever come this way is water.”

  He asked me for the radiation meter, and he checked the rock. The little red numbers hardly changed at all as he held the sensor against the rock. Radioactivity was negligible—less than the background count up above. We checked the temperature for form’s sake. It was 5° C. A little warmth in the rock but nothing special. Gley managed to find a little fluff in the bottom of his packsack, and he let it go in mid-air. There was no significant air current.

  “Not very hopeful,” I observed.

  “The tunnel’s leveling off,” he said, absently. “There’s probably another cave-system at this level. We certainly aren’t down to the water table yet. The water comes down here—there must be some kind of sink that it goes to.”

  “Sure,” I said, unenthusiastically. “Probably just around the next corner.”

  And, as luck would have it, I was right.

  CHAPTER FOURTEEN

  This time it was no mere bubble but a real underworld. It was a place where we could walk upright through chambers with vaulted ceilings on floors that were more or less level. There was no knowing how far the system extended, but there seemed to be caves and grottoes in great profusion. As we moved from one to another I had to keep scoring the rock with the point of a piton in order that we might find our way back. The shape of the chambers was irregular, and the ceilings especially were pitted and hollowed. There were crevasses in the floor which had to be avoided—most too narrow to fall down but nonetheless a cause of anxiety. From the lips of the cracks which ran across the ceilings hung stalactites—not in great profusion, but often impressive in their bulk. There were far fewer stalagmites, but here and there where water dripped perpetually a squat, rounded growth made its lazy way up toward its more graceful partner. I noted that several of the longer and thinner stalactites had shattered—sometimes the debris lay scattered below, more often it had been carried away by water into one or another of the abyssal cracks. Obviously the world down here was not untouched by the occasional earth tremors.

  There were pools of water here, looking quite placid and lifeless. No light ever reached here, nor was there any significant warmth in the rocks. The only energy supply was the rotting debris carried down from above, and that was frugal. Most of it was washed into the pits—little enough became mud at the bottom of these pools. Even at the micro-organic level there was probably hardly any life at all in the water.

  Some of the bigger pools, however, had rather more mud and offered rather more scope. The tunnel by which we had gained access to the system had come in almost horizontally, so that the torrents of water it occasionally carried would have gushed out over the floor to fill a dozen or more cracks, spreading its bounty thinly. But where any significant amount of water poured down from above it could eat out a bowl for itself which could grow deeper and deeper. There a thick silt might collect while only water carrying a light colloidal suspension of soil might flow out over the rim to disappear into the depths.

  Where the rocks had not been worn smooth by water they were often covered with a sheen of lustrous crystals and pockmarked with small blisters, but whether this was due to the solidification of lava long ago or to the fact that the crystalline elements in the matrix resisted erosion to a greater extent I was unable to tell. Sometimes the bedrock formed spirals and fringes around particular spurs of harder mineral, but I was at a loss to explain how it had occurred.

  We made much slower progress now, not because the way was difficult but because Gley was so intent on examining the surroundings. He dropped fragments of broken stalactite into some of the wider crevasses, and once or twice we heard them splash into water rather than rattling on rock. There was not much farther down to go. If we were to find anything it would have to be here. I had long ago lost my sense of direction, but Gley told me that in his opinion we were now working our way back from the direction of the mountain toward the rock vertically beneath the crater. Whether this was knowledge or optimism speaking I couldn’t tell.

  Periodically we checked the temperature of the air and took radiation counts. Soon we began to notice a change, albeit a slight one, as both began to rise very slowly. We were moving toward warmer rock, and perhaps getting closer to some subterranean source of radioactivity. We adjusted our direction to follow the guidance of the thermometer and the meter, and the hours slid past while we scored the rocks and gradually came into a slightly more hospitable region.

  We came into a series of larger caves, whose walls were streaked with colors, often forming aesthetically pleasing abstracts which lured the eye to follow them in a hopeless search for pattern, shape or meaning. The crystals began to take on the aspect of galactic clusters of stars in my overactive imagination, and the blisters and pores became mysterious universal entities for which there were no names. My attention, I fear, wandered perpetually from the task of searching the cracks and crevices of the floor in case by some serendipitous miracle we should find a plastic ray gun or some other esoteric product of a long-lost surface civilization. My dereliction of duty was, however, compensated by the zeal of Gley’s anxious gaze, which was everywhere in search of our ow
n crazy version of Man Friday’s footprint.

  Then we came to the greatest chamber of all, and found what we had been looking for. I had not known, really, until we saw it, that it was what we had been looking for, but the logic was ready-formed in my head when I saw it. It was a pool of vast proportions—more than a hundred meters across. It must have been very deep in the middle. Around its rim I could see four or five places where water might flow out as it was filled up, but the important thing was that there was a steady stream of water running even now from a ring of stalactites set high in the roof of the cave. That ring of stalactites, I knew, surrounded a hole more than a meter across. At the moment there was only seepage running down its sides—but when it rained the trickle would turn to a flood. It would be like turning on a tap. And if the passage were connected to one of the other fissures that opened into the floor and the rampart of the crater...what might not have fallen into the mud in the belly of this pool in ages past?

  I unslung my pack immediately. Gley was a little slower than I at realizing the significance of the pool, but when he realized I was not merely stopping for another rest he was quick to see the possibilities.

  “If we’d thought,” I said, “we could have brought fishing gear.”

  “I’ve got a crampon,” he said, digging out from his pack something that looked like a small grappling-iron. “It won’t pull out anything very small, but it might catch on something.”

  I was dubious. “I wouldn’t bank on finding any old boots,” I said. “Much better to wade out and fish up the mud in specimen bottles. We don’t have to find anything large. Something microscopic will do.”

  “We could dredge up a lot of mud and find nothing,” he pointed out.

  “You could throw that thing in a thousand times and not even catch a pebble,” I countered. “These suits are water-tight if we seal the filters in the helmet and attach oxygen bottles. They aren’t much for swimming in but we can probably manage. The helmets are a bit buoyant, unfortunately.”

  Meanwhile, Gley had another thought. He began unloading his packsack.

  “I can dredge up a sack full with this,” he observed, unnecessarily.

  It beat specimen bottles—especially when diving would be so difficult because of the helmets.

  “Okay,” I said. “Let me take it. I’ll fish up some silt and dump in beside the pool. You can sift through it. Then we’ll have more idea of what kind of wild goose chase we’re on.”

  I sealed the filters and attached an oxygen bottle. The oxygen was released slowly, mixed with the air that was trapped in the helmet. As oxygen was leaked slowly into it, the carbon dioxide and the organic material I exhaled would be slowly taken out by the same filtration system that made sure the air sucked in from outside was breathable. It wasn’t perfect but it worked well enough.

  With the empty sack in hand I waded out carefully into the pool. The bottom sloped appreciably but wasn’t ridged to any great extent. I trod on a pebble or two, but that merely reassured me that there was a lot of loose stuff trapped in the pool. When I was thigh-deep I bent over and submerged the sack. With some difficulty I managed to get it open reasonably near the floor of the pool, and then scraped it along. I could only feel an inch or so of sediment, but I did manage to scrape up a reasonable amount of it.

  When I took it back to the edge Gley looked at it with some disdain. He had cleared an area of almost flat rock, and when I tipped out the contents of the sack most of the water ran off immediately, whereas I kept the mud from returning to the pool with my forearm.

  “You’ll have to do better than that,” he said.

  “I will,” I assured him. “But let’s not let our ambitions run too far ahead.” I was already stirring the silt with my fingers. He brought the lamp up close and began to do likewise. Two fingers was just about enough to handle the job. The particles were finely divided indeed. There was nothing at all of any appreciable size.

  Gley gave up in disgust after no more than a few seconds. He turned away and picked up the radiation meter. He brought the sensor close to the silt, and immediately the numbers began to change. They weren’t exactly dancing, but they were doing more than they’d done before.

  “It’s radioactive,” he observed, the excitement in his voice making it sound as if we were on the brink of a magnificent discovery.

  “About as radioactive as the luminous paint on the hands of my watch,” I mused. “Except that there’s a lot more of the mud. A great deal more. It’s not just the vegetable matter in the dust that’s decaying.”

  “Something between here and the surface is radioactive,” said Gley, his voice slightly unsteady. “The water leaches through, brings finely divided particles down.”

  I could see what he was thinking. The mysterious atomic pile embedded in the rock, inaccessible to everything but the seeping water, being carried away grain by grain. It might just be true—provided that the pile had decayed virtually to extinction. Even finely divided grains of uranium or plutonium should be a hell of a lot hotter than this was. But if there had been a pile, and it had cooled down, then there ought to be all kinds of things in the silt. All the breakdown products. And from a comparison of the density of the radioactive isotopes with the density of the breakdown products in the mud, one might be able to work back to an estimate of the time it had taken for the original materials to break down. In fact, with a little bit of sophisticated detective work using the apparatus Linda was guarding up in Gley’s cabin it could well be possible. It wasn’t much of a clue, but a clue it was. Provided we were prepared to assume that the original radioactive substance had come from a reactor rather than from natural ore. If it had.

  “I’ll try to get some mud from farther out,” I said, turning back to the pool. I waded slowly out toward the middle of the pool again. This time I let the water come up to my chest before I stopped. I was now about twenty meters from the side of the pool. As I’d anticipated, I had difficulty ducking, and it wasn’t easy operating in the darkness. Gley was holding up the lamp but that was a long way away now, and its light made no impression below the surface. However, I managed to crouch down long enough to get the sack down into the mud, which was quite a lot deeper here. As I moved it around, my arm brushed a couple of large, rounded stones, and then something else that was longer and thinner. I managed to get my fingers around it before standing upright again, but in so doing I let a little of the mud out of the sack.

  What I’d grabbed was white, though somewhat slimed with black and green. It was a bone—the lower half of the femur of a donkey. I carried it back along with the specimen of silt.

  Again there was nothing in the mud that looked interesting to the naked eye. Gley loaded it carefully into a specimen bottle.

  “How old’s the bone?” he asked, after I’d reassured him that it couldn’t possibly be part of a Set, let alone an alien.

  “Can’t tell,” I told him. “But not very old. As I said, with sulfur dioxide dissolved in the water the pool’s a weak acid-bath. In time it would soften the bone, and in the long run it’ll eat it away altogether. This is still rigid. Probably not more than ten years old. Possibly a hundred. Not a thousand...but even if it were, what would it prove?”

  “It proves that things which are quite large can get down here,” he said. “So somewhere in there....”

  I took the point. I turned to go back for another shipment of mud. Then Gley let go a wordless exclamation. I thought he’d found something, but when I looked round he was bolt upright, listening.

  “Did you hear that?” he asked.

  “Stand still. Listen.”

  I stood perfectly still. The silence seemed infinite. But then there was something—first it was so slight that I was prepared to credit it to my imagination, but then it was repeated.

  It was a scraping sound. At first I couldn’t conjure up an idea to fit it, but I knew it had to be something scraping on stone. Something hard, I thought, but not metallic. Like the sound of a leat
hery boot...or a leathery foot.

  Gley set down the lamp and lifted the flashlight, whose beam could reach further. He began to shine it around in a long, slow arc. I could see nothing, but I heard the sound again.

  With his other hand, Gley reached, for his gun—the massive shotgun that he had brought down because it made him feel safer to be carrying it. Right at that moment I was glad he had it.

  “The thing doesn’t like light,” I said. “If this is its territory it’s probably blind, or so nearly so that light is just a dazzling pain.”

  I wanted to add that logically it should stay away, but I wasn’t so sure of that. If it was truly blind maybe the light wouldn’t bother it much. And if this really was its territory then we, as invaders, were inviting attack.

  The sound came again, louder now, and then again from somewhere else. Gley tried to catch it with the light, but there was nothing but shadows.

  “It moves very fast,” said Gley.

  “No,” I replied, feeling my heart sink a little further. “There are two. At least.”

  Then the light, darting quickly to the source of another sound, picked up a shadow that fluttered.

  “Bats,” I said. “It’s not just one predator, it’s a flock. Tiny teeth...claw marks but no feet. It didn’t have to be big to strip a Set that fast...just numerous.”

  It dawned on me suddenly that what had seemed like an enigma was no puzzle at all. We had been stupid to think of one organism when the analogy was there all the time. It isn’t the big cats that strip carcasses to the bone in a matter of minutes back on Earth. The only creature which does that is a fish the size of a man’s hand—the piranha, which has tiny little teeth and which hunts in shoals. The sound of leather on stone wasn’t made by boots or feet...it was made by wings. Flying piranhas.

  I took one step back toward the side of the pool. Then I stopped, as the light caught more fluttering shadows. They were taking to the air. They moved as a group, quite soundless in flight. Even their echo-location noises were far too high-pitched for human ears to catch. For a few moments there wasn’t much purpose in their fluttering, but now that they were airborne they were obviously not going to go back whence they came.