They looked down from their point on the high ledge into the length of the cleft-world. A very faint light streak could be seen looking upward—this was the curious volcanic glass of the surface roof. Through it penetrated just a hint of the full Earthlight that bathed the outer moonscape. Down were shadows and darkness, in the distance little bits of moving lights, flickering sparks, that may have been the Glassies' head-stalks.

The two men used their remaining flashlamp to light up the narrow ledge. Carefully they made their way down the steep side of the cavern wall, their light swinging slowly back and forth. "Suppose the Glassies see the light?" said Peter. "We may be in for trouble."

"Maybe," said Robin, "but this time we'll be alert for it. We'll have to steer clear of overhanging spots, keep our light swinging about, but I have an idea we'll have no trouble. That bomb and the shooting will probably make them keep their distance."

Down they went until they reached the level surface. Then they started off across the space to the faraway place where the lights could be seen. It was the winter half-month now for the sublunar world. The Moon growths had fallen, shriveled, died. Their seeds lay dormant for the next sun period. It was fairly chilly in the cavern, yet not as cold as it might have been. Somewhere, thought Robin, there is a warm volcanic current keeping this cavern from freezing over.

They kept a good distance between each other, the long, thin, strong cord linking them being kept almost taut. The reasoning behind this was that if another lassoing attempt were made, it would be almost impossible to get both at once. As long as one were free to get at his firearms, they could overcome such an attack.

On they went, with still no sign of meeting any opposition. Then Robin saw a sudden faint flicker in a clump of darkness to one side. He stopped, whispered into his helmet-radio what he had seen. Rapidly his eyes swept the scene, and, yes, there was another suddenly doused flicker on the other side. The Glassies must be watching them, waiting.

Now the two proceeded at a slow pace, widely swinging their light from side to side to prevent ambush. "Somehow," said Robin, "we are going to have to prove we're friendly. We may have to live here a long time."

"Yes," said Peter, "but how?"

They walked only a few steps farther before the answer was given them. Something was standing directly in their path. As their light swung near it, this figure raised two hands high and its head-stalk light flashed into brilliant prominence.

It was a Glassie standing there, a transparent-bodied Moonman whose odd face bore the equivalent of a broad smile and whose chest was decorated with a painted black circle. Robin stared at the figure of this chief a moment. He saw something move on the Glassie's shoulder—a tiny, dark, manlike creature no bigger than a doll.

This creature opened its mouth, uttered a sharp shriek. "Cheeky!" gasped Robin. And at the sound of his voice the little monkey leaped from the Glassie's shoulder in one monstrous Lunar bound and arrived at Robin's foot. Another jump and it was in Robin's arms, screeching with joy.

The Glassie chief came forward. It spoke, "Robin! Good see you. Good see you." It was Korree! Now he too moved forward to grasp Robin awkwardly but happily ... Korree wearing the marking of the tribal head!

Now other Glassies appeared around them, but they held no weapons in their hands, no sticky hoops or bindings. They stood around the newcomers with awe and uncertainty—willing to be guided by Korree's actions but aware of the possible results of an encounter with space-suited Earthlings.

Korree turned a moment, waved them on, speaking in their tongue. Peter came up, nodding, shoving his pistol back into its holster.

"I see your two friends have won the day while we were up above," he said. "They were indeed friends."

The two brothers were escorted back to the site of the native settlement in a crowd of bobbing head-stalk lights and jabbering Glassies. Korree explained as they walked.

It seemed that the explosion of the homemade bomb had completely disrupted the fear in which Von Borck had held the Glassies. This was greater magic to them, and it was the mysterious little being—Cheeky—who had accomplished it. In the first excitement, the Glassies had fled and hid. That was when the German had come after Peter and Robin, leaving the Glassies behind.

This, too, was an indication that even the powerful stranger who had usurped the role of chief by the expedient of his mere existence and strength had bowed to the power of the little monkey. In Moonman tribes, the chief never fled the scene of his authority. To do so was to abdicate it. Von Borck had unknowingly destroyed his authority by his abrupt chase after Robin and Peter.

When Korree made his way back to the cave-village after giving up his attempt to follow his Earthling friends, he had arrived to find the Glassies cowering in fear of the capering Cheeky, who was unhurt by the blast.

Korree had gathered up Cheeky in his arms and by so doing had made himself the master of the situation. That was how it came about that the two brothers had been met by a friendly admiring reception rather than a hostile one.

"But what happened when Von Borck returned here to get his space suit?" asked Robin.

Korree waved a hand as if the answer was obvious. "Glassies hide," he said simply. "Korree hide. Cheeky hide. Everyone hide." And so Von Borck arrived to find himself deserted and unwelcome. And he had promptly left to follow the trail to the surface.

Once back at the site of the caves, they found themselves honored guests. In the days that followed, they set up a cave for themselves, organized a home. Cheeky seemed to have now attached himself to Korree and went everywhere with the Glassie. Robin and Peter rested, set up a regimen of native food, observed the Glassies' way of life.

The sun came up again on the surface and flooded the cleft with its light. The Moontrees grew rapidly in dense profusion. The two brothers gradually explored the length and breadth of the little world, systematically working around it in search of some new path upward.

But their search seemed fruitless. There were a number of holes and breaks in the walls and caves, but none promised a place of exit to the surface.

They went back to the original ledge and tunnel, tried to work their way in, but it was blocked with fallen stone and jammed too tightly for passage.

They discussed the possibility of making explosives, blasting through, but discarded this as they realized the basic fragility of the whole cleft setup. Such blastings might do worse damage, might even crack a direct opening to the surface through which the air within the cleft-bubble would rush out, leaving it a sterile, cold, and dead region.

Finally after another Lunar night and another Lunar day, exhausting still one more Earth month, they settled down to a slow steady picking and shoveling. They worked in the blocked tunnel in all their spare time, carefully picking away chips of rock, pushing others aside, burrowing around fallen slabs, slowly, gradually, painfully working their way along the old path. But it was hard and unrewarding work. It went slowly and they were always afraid of a cave-in.

Two or three times such an event did occur, and had it not been for the slowness with which things fell on the Moon, one or the other brother would surely have been pinned down. On the third such disaster, the two quit the task, returned to their home in the Glassie village discouraged.

"This will not work," said Robin. "We'll have to give up this entire approach. It would be months or even years before we could make our entire way and by that time one of us would surely be killed in the tunnels. They are still highly unsettled, still shifting."

They sat down, looked at each other. "There must still be a way," said Peter. "We must find a way to reach the surface. Otherwise we will remain here forever."

Robin nodded, deep in thought. Another night was coming over the cleft. The sun was passing swiftly from overhead. A chill began to touch the air, as darkness blacked out the cavern. It would be another two weeks before they could resume any work on their problem. Robin started to build a fire in their cave, one they burned every Moon winter's night. As he did so a thought struck him.

He turned. "When we were first returning from the surface it occurred to me as we came out that there had to be some sort of volcanic current warming this cavern, sun or no sun. Now it seems to me that if we could find that current, we would find some sort of air stream or water stream, that must go upward. We ought to look for the warmest spot in the cavern, trace it."

Peter turned, a sharp light in his eye. "And now that you say it, do you know what that current is? It's the one that passes the break in the crater wall—the constant hurricane that we broke through to get in here, which rushes by the break so hard and so fast that it seals this cavern's quiet inner air as perfectly as if it were an air lock. It has to be that very current which passes somewhere lower down and warms this cleft!"

Robin nodded, a sharp excitement stirring him. "I think we have hit on it. The night time is the time to hunt for it. Find the spot or places in this cleft that stay warmest and they must be nearest the underground wind tunnel."

So they set out on a new course of exploration, this time scouting the bubble in the dark of the night. It grew chillier, but in their space suits, which they had resumed for this expedition, they could keep warm. They found several areas along the ground where it seemed a bit warmer than in the cave generally, but after several days of search, this clue also seemed fruitless. The areas were such that no amount of digging short of high explosives would suffice.

Finally when the long Lunar night was almost over, they awakened from sleep in the cave to face the thought that this too was a blind alley. Korree entered, the monkey on his shoulder. He made his way to them, noticed their air of sadness, asked them why.

Tired, Robin explained to him what they were looking for. His Glassie friend cocked his head. "You come my home. I show you hot spot," he said.

The two men looked up. "What?" asked Peter. Korree repeated his statement. Peter looked at Robin quizzically. Without another word the two got up and followed the Glassie.

The deep cave where the chief made his home was only a short distance from their own. Here, at the very back of the chief's home, they found what they sought. There was a thin, sharp crack in the rear wall. The stone around it was definitely warmer than that in the rest of the cave. Putting their ears to the crack, they could hear the faint high whistling of the air current that must be roaring past only a foot or two beyond.

"This is why it was picked as the chief's cave," said Robin. "It's practically air-conditioned!"

The next day, after the sun had finally made its appearance, the two started to work in the back of Korree's cave. They worked carefully with axe and pick, enlarging the crack, chipping away at it. Finally, they dislodged a sizable segment of rock, enough to allow one man to squeeze through.

Sure enough, there was a dark underground channel through whose center rushed the eternal current of hot volcanic air. This channel probably had its source somewhere in the still-mysterious depths of the Moon's core. It wound and forced its way upward doubtless to dissipate somewhere, as the cold of the surface bore away its warmth, probably to wind up downward again as a mass of cold gas.

There was barely enough room at the side of the tunnel for a man to stand flat against the wall, without touching the blast.

Robin, who had gone through to examine it, came back out into the light of Korree's cave. "Well," he asked Peter, "what do we do now?"

His brother nodded. "I think we can get to the surface all right. Just get in the blast and let ourselves be blown along upward. When we find that break, we'll get out of the current and we'll be able to reach our rocket."

"Uh huh," said Robin, "and then how do we get back down here again?"

Peter shrugged. "I don't know. There must be a way."

The two returned to their own place and talked it over. But the opportunity was too good to pass up. "Sooner or later," said Robin, "we're going to do it. So we may as well face that. As for getting back, perhaps we could simply walk all the way down the channel, keeping carefully to the side of dead air just beyond the blast."

Peter frowned. "I don't think you'll find much of that. There can't be many places where such a dead air channel exists. On the other hand, if we attack the problem of returning by the old route, we may be able to find a way through it from that end—or make a new one. Back at the rocket there are explosives, better tools than those we have. I think we should risk it."

"Yes," Robin added, "I think so too. Besides, we ought to fire off some more flares. Our signals may never have been seen."

That being settled, the two Earthlings again donned their space suits, equipped themselves, tied themselves together with a length of cord. They returned to Korree's cave, explained their project and gravely shook hands with their Glassie friend.

Then Robin carefully eased himself through the break into the dark channel. Peter squeezed through after him, as Robin flattened himself along the wall and moved aside. Their helmets sealed, Robin counted to three, and then both leaped forward.

Instantly the racing wind current caught them up, snatched them off their feet. They found themselves being blown madly along the darkness like leaves before a gale.

The air was hot and Robin felt himself almost scorched as he was hurled along, his elbows and legs occasionally scraping the wall, once feeling himself somersaulting upward, twisting and turning in the horrible blast.

For a dreadful moment he felt panicky, out of control, utterly helpless in the grip of the underground tornado. He lighted the flash, saw it wildly flickering. He drew his legs up, ducked his head, and found he could get his equilibrium. Ahead of him the tunnel was ascending. He felt himself rising, felt the slight drag occasionally at his belt as Peter's bouncing body followed his.

Now the air began to cool and seemed to slow down slightly. The passage leveled off, he was whirling down a straight passage, and suddenly, in a split second of awareness, he saw a faint spot of bright light ahead of him. He rushed toward it, like a ball buoyed on a stream from a fire hose. It must be the exit to the surface, he thought, and in a second held out the axe he gripped in his hand.

The handle caught at the opening as he went sailing by, jammed, swung his body against the wall with a smack. Peter's body flashed past, caught up short by the cord, and also hit the body of airless space on the outer side of the channel.

They climbed dazedly to their feet and struggled to the narrow break. They staggered out onto the surface, now bathed in the blindingly brilliant light of the sun rising over the peaks of the farther mountains ringing the crater.

Around them were the first shoots of the stubborn and hardy surface vegetation in this crater, dwarfed cousins of the plants below.

They caught their breath. "Better get moving," said Peter finally. "This sun is dangerous."

They started across the floor of the crater, the several hundred feet to where the nose of the wrecked Russian rocket rested. Both men knew they were bruised from the short, mad trip. There would be scraped shins and knees and elbows. But they had made it, that was the thing.

They were about a hundred feet out, when suddenly Robin stopped, stared into the sky. Peter followed his glance.

There was something up there. When they had first glanced up, there was the Earth still in its place, though now but a crescent. There were the myriad stars, and the corona-encircled sun. And now there was another celestial object. A tiny spot of reddish orange was growing in the sky, growing as they watched it.

"What is it?" asked Robin in a half whisper, afraid to venture the thought that was rioting around in his head.

Peter simply stared, transfixed.

The moving spot of fire grew rapidly, enlarged, took shape. It was a tiny stream of energy, like the tail of a tiny comet. It came still closer. Now they could see a flash of white and silver at its core, and still it drew closer. Now it took definite shape, a tiny body of metal and paint riding down on a long stream of atomic fire!

Then in mere seconds it hung over them, no longer tiny but a giant tower of polished metal hanging over the crater floor, falling ever more slowly, its great column of rocket fire reaching and scorching the surface of the rock. And suddenly, the fire was gone, there was a faint thud felt through the ground, and the two brothers stood staring.

Out there, not very distant, was standing a glorious, tall, slender rocket ship, fresh with paint, beautifully and delicately balanced on finely tapered fins, graceful as only a space craft can be.

On its side, clearly visible in the sunlight, was a large blue circle on which was superimposed the white star of the United States Air Force. There were numbers and things and a small, black air lock now opening near the nose of the rocket, but Robin and Peter hardly noticed these through the tears of joy that sprang to their eyes as they ran and bounded over the Moon's surface to greet their rescuers. Waving their hands, shouting, heedless of whether they were being heard, they were Robinson Crusoes no longer. They were on their way home.

ABOUT THE AUTHOR

Donald A. Wollheim, born in 1914, has lived in New York City all his life. At first a free-lance writer of stories and articles mainly for science-fiction magazines, he began his career as editor in 1940. He has edited all kinds of magazines, including detective, sports, and western periodicals. In 1952, Mr. Wollheim was invited to launch Ace Books and has since held the position of editor of these paperbacks.

Science fiction is Mr. Wollheim's chief interest and hobby. His collection of science-fiction books and magazines is one of the largest and his list of published books is a long one. Many distinguished anthologies of fantasy and science fiction bear his name as editor. Among his most recent books of original fiction are The Secret of Saturn's Rings and The Secret of the Martian Moons.