Hilvar scarcely heard the words Alvin whispered as walked slowly back to the ship.

«I hope they got home,» he said.

«And where now?» asked Hilvar, when they were once more out in space.

Alvin stared thoughtfully at the screen before replying.

«Do you think I should go back?» he said.

«It would be the sensible thing to do. Our luck may ad hold out much longer, and who knows what other surprise these planets may have waiting for us?»

It was the voice of sanity and caution, and Alvin wad now prepared to give it greater heed than he would have done a few days before. But he had come a long way, and waited all his life, for this moment; he would not turn bar while there was still so much to see.

«We’ll stay in the ship from now on,» he said, «and wn won’t touch surface anywhere. That should be safe enough surely.»

Hilvar shrugged his shoulders, as if refusing to accept any responsibility for what migt happen next. Now that Alvin was showing a certain amount of caution, he thought it unwise to admit that he was equally anxious to continu! their exploring, though he had long ago abandoned all hopl of meeting intelligent life upon any of these planets.

A double world lay ahead of them, a great planet with 1 smaller satellite beside it. The primary might have been the twin of the second world they had visited; it was clothed it that same blanket of livid green. There would be no point it landing here; this was a story they already knew.

Alvin brought the ship low over the surface of the satellite, he needed no warning from the complex mechanism which protected him to know that there was no atmosphere here. Al shadows had a sharp, clean edge, and there were no gradation between night and day. It was the first world on which he had seen something approaching night, for only one of the more distant suns was above the horizon in the area where they made first contact. The landscape was bathed in a dull rep light, as though it had been dipped in blood.

For many miles they flew above mountains that were sti) as jagged and sharp as in the distant ages of their birth. This was a world that had never known change or decay, hay never been scoured by winds and rains. No eternity circuit were needed here to preserve objects in their pristine fresh ness.

But if there was no air, then there could have been no life -or could there have been?

«Of course,» said Hilvar, when Alvin put the question d him, «there’s nothing biologically absurd in the idea. Lift can’t originate in airless space-but it can evolve forms that will survive in it. It must have happened millions of times, whenever an inhabited planet lost its atmosphere.»

«But would you expect intelligent life forms to exist in a vacuum ? Wouldn’t they have protected themselves against the loss of their air?»

«Probably, if it occurred after they achieved enough intelligence to stop it happening. But if the atmosphere went while they were still in the primitive state, they would have to adapt or perish. After they had adapted, they might then develop a very high intelligence. In fact, they probably would-the incentive would be so great.»

The argument, decided Alvin, was a purely theoretical one, as far as this planet was concerned. Nowhere was there any sign that it had ever borne life, intelligent or otherwise. But in that case, what was the purpose of this world? The entire multiple system of the Seven Suns, he was now certain, was artificial, and this world must be part of its grand design.

It could, conceivably, be intended purely for ornament to provide a moon in the sky of its giant companion. Even in that case, however, it seemed likely that it would be put to some use.

«Look, said Hilvar, pointing to the screen. «Over there, on the right.»

Alvin changed the ship’s course, and the landscape tilted around them. The red-lit rocks blurred with the speed of their motion; then the image stabilized, and sweeping below was the unmistakable evidence of life.

Unmistakable-yet also baffling. It took the form of a wide-spaced row of slender columns, each a hundred feet from its neighbor and twice as high. They stretched into the distance, dwindling in hypnotic perspective, until the far horizon swallowed them up.

Alvin swung the ship to the right, and began to race along the line of columns, wondering as he did so what purpose they could ever have served. They were absolutely uniform, marching in an unbroken file over hills and down into valleys. There was no sign that they had ever supported anything; they were smooth and featureless, tapering very slightly toward the top.

Quite abruptly, the line changed its course, turning sharply through a right angle. Alvin overshot by several miles before he reacted and was able to swing the ship around in the new direction.

The columns continued with the same unbroken stride across the landscape, their spacing perfectly regular. Then, fifty miles from the last change of course, they turned abruptly through another right angle. At this rate, thought Alvin, we will soon be back where we started.

The endless sequence of columns had so mesmerized them fat when it was broken they were miles past the discontinuity before Hilvar cried out and made Alvin, who had noticed nothing, turn the ship back. They descended slowly, and they circled above what Hilvar had found, a fantastic picion began to dawn in their minds-though at first neither dared mention it to the other. Two of the columns had been broken off near their base and lay stretched out upon the rocks where they had fallen. Nor was that all; the two columns adjoining the gap had bent outward by some irresistible force.

There was no escape from the awesome conclusion. Alvin knew what they had been flying over; it was so thing he had seen often enough in Lys, but until this mom the shocking change of scale had prevented recognition.

«Hilvar,» he said, still hardly daring to put his thou into words, «do you know what this is?»

«It seems hard to believe, but we’ve been flying aro the edge of a corral. This thing is a fence-a fence l hasn’t been strong enough.»

«People who keep pets,» said Alvin, with the nervous lain men sometimes use to conceal their awe, «should make sure they know how to keep them under control.»

Hilvar did not react to his forced levity; he was staring the broken barricade, his brow furrowed with thought.

«I don’t understand it,» he said at last. «Where could have got food on a planet like this? And why did it bred out of its pen? I’d give a lot to know what kind of animal was.»

«Perhaps it was left here, and broke out because it ail hungry,» Alvin surmised. «Or something may have made it annoyed.»

«Let’s go lower,» said Hilvar. «I want to have a look the ground.»

They decended until the ship was almost touching barren rock, and it was then that they noticed that the ply was pitted with innumerable small holes no more than an inch or two wide. Outside the stockade, however, the groud was free from these mysterious pockmarks; they stopped ruptly at the line of the fence.

«You are right,» said Hilvar. «It was hungry. But it wash an animal: it would be more accurate to call it a plant. had exhausted the soil inside its pen, and had to find fry food elsewhere. It probably moved quite slowly; perhaps took years to break down those posts.»

Alvin’s imagination swiftly filled in the details he could never know with certainty. He did not doubt that Hilvars analysis was basically correct, and that some botanical monster, perhaps moving too slowly for the eye to see, had foul a sluggish but relentless battle against the barriers that hemmed it in.

It might still be alive, even after all these ages, rovin will over the face of this planet. To look for it, now, would be a hopeless task, since it would mean quartering the surface of an entire globe. They made a desultory search in the few square miles around the gap, and located one great circular patch of pockmarks almost five hundred feet across. where the creature had obviously stopped to feed one could apply that word to an organism that somehow drew its nourishment from solid rock.