[Illustration: He staggered back from the lapping pool--the gas--the weight of the girl’s body--the dog--]

Here the dark cave, along which Nat Starrett had been creeping, broadened into what his powerful searchlight revealed to be a low, wide, smoothly circular room. At his feet lapped black, thick-looking waves of an underground lake, a pool of viscous substance that gave off a penetrating, poignant odor of acid, sweetish and intoxicating, unlike any acid he knew. The smell rolled up in a sickening, sultry cloud that penetrated his helmet, made him cough and choke. Near its center projected from the sticky stuff what appeared to be the nose of a spaceship.

He looked down near his feet at the edge of the pool where thick, slowly-moving tongues of the liquid appeared to reach up toward him, as if intent on pulling him into its depths. As each hungry wave fell back, it left a slimy, snake-like trail behind.

Now came a wave of strange music, music such as he had never heard before. Faintly it had begun some time back, so faintly he was barely aware of it. Now it swelled into a smooth, impelling wail lulling him into drowsiness. He did not wonder why he could hear through the soundproof space helmet he wore; he ceased to wonder about anything. There was only the strange sweetness of acid and the throbbing music.

Abruptly the spell was broken by something shrilling in his brain, sending little chills racing up and down his spine. Digger! A small, oddly canine-like creature with telepathic powers, a space-dweller which men found when first they came to the asteroids. The relationship between spacehounds and men was much the same as between man and dog in the old, earthbound days. Appropriate name for the beast, Digger. With those large, incredibly hard claws, designed for rooting in the metal make-up of the asteroids for vital elements, the spacehound could easily have shredded the man’s spacesuit and helmet, could, at any time, tear huge chunks out of men’s fine ships.

The half-conscious man jerked his thin form erect. His mouth, which had gaped loosely, closed with a snap into firm lines.

“She isn’t in this hell hole, Digger. You wouldn’t expect her to be where we could find her easily.”

Scooping the small beast up under his good arm, he quickly climbed the steep, slimy slope of the cave. The other arm in his suit hung empty. That empty arm in the spacesuit told the story of an earthman become voluntary exile, choosing the desolation of space to the companionship of other humans who would deluge him with unwonted sympathy. The spacehound was friendly in its own fashion; fortunately, such complex things as sympathy were apparently outside its abilities. The two could interchange impressions of danger, comfort, pleasure, discomfort, fear, and appreciation of each other’s company, but little more. Whether or not the creature could understand his thoughts, he could not tell.

As he went on, he reviewed, mentally, the events leading up to his landing here. The sudden appearance on his teleview screen of the face and slim shoulders of a girl. Her attractiveness plainly distinguishable through her helmet; for a moment he forgot that he disliked women. The call for help, cut short ... but not before he had learned that apparently she was being held prisoner on Asteroid Moira. He knew he’d have to do what he could even if it meant unwonted company for an indefinite length of time. The spell was gone soon after her face vanished; he remembered former experiences with attractive-looking girls. Damn traditions!

A change in his course and a landing on Asteroid Moira. Here he’d found a honeycomb of caves, all leading from one large main tunnel. The cavern walls had been of a translucent, quartz-like substance, ranging in color from yellowish-brown to violet-grey. It looked vaguely familiar, yet he could not place it. There was not time to examine it more carefully.

The room in which he’d found the evil, hungry lake had been the first one to the right. Now he crossed to the opening in the opposite wall. The mouth of this cave was much larger, wider than the other. He stood in the opening, slowly swung the beam of his torch around the smooth walls, still holding Digger, who, by now, was indicating that he’d like to be set down. Nat released him unthinkingly, his mind fully taken up with what the light revealed.

Spaceships! The room was packed with them--all sizes, old and new. A veritable sargasso. At first, he thought they might be craft belonging to nameless inhabitants of this world, but, as he approached them, he recognized Terrestrial identifications.

The first was a scout ship of American Spaceways! Nat recognized the name: Ceres, remembered a telecast account of its disappearance in space. There was a neat little reward for information as to its whereabouts. Nat’s lips curled in derision: it wouldn’t equal the expense of his journey out here. There was a deep groove in the smooth material of the floor where the ship had been dragged through the doorway into the room. What machines could have done this work without leaving their own traces? He went to the other ships: all were small, mostly single or two-passenger craft. The last entry in the logs of many was to the effect that they were about to land on the Asteroid Moira to rescue a girl held captive there.

None had crashed; all ships were in perfect order. But all were deserted. Two doors were gone from the interior of one of the vessels. They might have been removed for any of a hundred reasons--but why here?

Nat’s glance swept the room, came to rest on the figure of a heavy duty robot of familiar design. Semi-human in form, it looked like some misshapen, bent, headless giant. He inspected it: Meyers Robot, Inc. Earth designed for mining operations on Mars.

“Well, Digger, I can see now how these ships were brought in here; that robot could move any one of these with ease. But that doesn’t explain where the humans have gone. It might be space pirates using this asteroid for a base, or it might be some alien form of life. We’re still free. Shall we beat it or stay and try to check this out?”

He did not know how much of this got over to the spacehound, but the impressions he received in answer were those of approving their remaining where they were.

“I suppose the best system is to explore the rest of the caves in order; let’s go.”

Followed by Digger, he walked quietly toward the next cave on the left, slipped through the doorway, and, standing with his back against the wall, swung the light of his torch in a wide, swift arc about the room. Halfway around, he stopped abruptly; a slim, petite figure appeared clearly in the searchlight’s glare. The girl he had seen on the televisor stood in the middle of the room, facing a telecaster, her back toward him. She did not seem aware of him as he moved forward. What could be wrong; surely that light would arouse her.

The figure did not turn as he approached. So near was he now that he could seize her easily, still she made no move. Nat stepped to one side, flashed his torch in her face. Her beautifully-lashed eyes stared straight ahead unblinkingly; the expression on her lovely composed face did not change. A robot! He laughed bitterly. But then, he was not the only one...

She was an earth product; Nat opened her helmet and found the trade-mark of Spurgin’s Robots hung like a necklace about her throat. But whoever had lured him here easily could have removed her from one of the vessels in the front cave. It did not seem like the work of pirates, more likely unknown intelligent beings.

He turned to examine the televisor. It, too, was an earth product. The mechanism was of old design; evidently it had been taken from the first of the ships to land here. Outside of the telecaster and the solitary robot, there was nothing to be seen in this cave.

A sound behind him. He whirled, heat-rod poised for swift, stabbing action. Nothing--except--small bowling-ball things rolling in through a narrow door. Ridiculous things of the same yellowish-quartz material as composed the cave-walls. At regular intervals a dull, bluish light poured forth from rounded holes in their smooth sides. And issuing forth from within these comic globes was the same weird, compelling music he had heard before. They rolled up to him, brushed against his toes; a shrilling in his brain told him that Digger was aware of them.

“Back, Digger!” he thought as he drew away from the globes. They poured their penetrating blue light over him, inspectingly, while the music from within rose and fell in regular cadences, sweetly impelling and dulling to the senses as strong oriental incense.

But Digger was not soothed. The spacehound lunged at one of the globes; instead of slashing its sides, he found himself sailing through the air toward it. Nat received impressions of irritation combined with astonishment. Within the globes, the music rose to a furious whine while one of the things shot forth long tentacles from the holes in its side. Lightning-swift they shot forth, wrapped themselves about the body of the spacehound, constricting. Digger writhed vainly, his claws powerless to tear at the whip-like tentacles. Nat severed the tentacles at their base with the heat-beam.

He turned, strode toward the door watching the spheres apprehensively out of the corner of his eye, ready to jump aside should they roll toward him suddenly. But they followed at respectful distances, singing softly.

Before he reached the door, he found himself walking in rhythm to the music, his head swaying. It came slowly, insidiously; before he was aware, his body no longer obeyed his will. Muscles refused to move other than in coordination with the music. His arm relaxed, the heat-rod sliding from his grasp.

But Digger! The spacehound sent out a barrage of vibrations that fairly rocked his brain out of his skull. Simultaneously, the beast attacked the nearest globes, tearing fiercely at them. Rapidly the others rolled away, but two lay torn and motionless, the music within them stilled.

Nat reached down, retrieved the heat-rod. “I think we’d better look for a ‘squeaker’. Next time they might get you, Digger.”

They returned to the room of the spaceships, seeking one of the small, portable radio-amplifiers used for searching out radium. It was known as a “squeaker” because of the constant din it made while in use; the noise would cease only when radium was within a hundred feet of the mechanism. He found one after searching a few of the smaller ships.

With the portable radio strapped to his back, power switched on, he started again down the main tunnel. The globes set up their seductive rhythms as before, but he could not hear them above the discord of his squeaker. Failing to lure him as before, they sought to force him in the direction they desired him to go by darting at him suddenly, lashing him with their tentacles. But it was a simple thing to elude them. Still remained the question: why could they want to lure him into that stinking pool of acid?

He flashed a beam of heat at the nearest of the annoying globes. Under the released energy it glowed, yet did not melt. But the tentacles sheared off and the blue lights faded. The flow of music changed to shrill whines as of pain and its rolling ceased. The others drew back; he turned down another tunnel.

They stopped at the cave beyond the one where he had found the robot-girl. It was sealed by a locked door, one of the airlock-doors from that space vessel, firmly cemented into the natural opening of the cave.

Nat bent forward, listening, his helmeted head pressed against the door. No sound. He was suddenly aware of the dead silence that pressed in on him from all sides now that the globes no longer sang and his “squeaker” had been turned off. The powerful energy of his heat-beam sputtered as it melted the lock into incandescent droplets which sizzled as they trickled down the cold metal of the door. The greasy, quartz-like material at the side of the door glowed in the heat from his rod, but no visible effect upon it could be seen. What was that material? He knew, yes, he knew--but he could not place a mental finger on it.

He thrust the shoulder of his good arm against the heavy door, swung it inwards, stepped inside. The light of his torch pierced the silence, picked out a human skeleton in one corner. He hurried toward it--no, it was not entirely a skeleton as yet. The flesh and bone had been eaten away from the lower part of the body to halfway up the hips, as though from some strong acid. The rest of the large, sturdy frame lay sunken under the remains of a spacesuit which was tied clumsily around the middle to retain all the air possible in the upper half of it. Evidently some acid had eaten away the lower half of the man’s body after he had suffocated. The face was that of a Norwegian.

By one outstretched hand a small notebook lay open with the leather back upward. The corners of several pages were turned under carelessly--Nat swung the torch around the room. It was bare. The notebook--quickly he picked it up. The page on which the writing began was dated May 10, 2040. About two months ago.