Robin had no time to wonder why he had not been instantly killed by the crash, because the explosion on hitting the surface of the dome was followed instantly by a tremendous roaring sound that surrounded the entire rocket nose. This was in turn accompanied by a powerful pressure on the rocket, which threw Robin against the nose-end cushioning and held him there.

The pressure was not steady, changing as the roaring itself changed, with sudden bursts of sound, convulsive shoves, and changes in pitch. The rocket was being slowed by a terrific outward burst of gases, gases that must have been imprisoned in a huge volcanic bubble whose outermost surface was the dome, so mysterious to Terrestrial observers. By bursting through the thin lava shell, Robin's rocket had released these pent-up gases and was boring its way down on its still rapid momentum against the pressure of this column of gas.

Robin did not know this at the time, though he figured it out later. At the time, he had all he could do to keep himself from being battered black-and-blue by the jolting rocket. He kept his head clutched tightly in his arms, rode with the bumps and roars, and tried to keep his breath from being knocked out of his lungs.

There was another violent shock and crack and again the rocket bounced to a new flow of gases. It had slammed through one huge bubble, breaking through the bottom shell only to burst into a lower pocket of gas. The roaring subsided to a lower pitch as the new gases did not find the near-vacuum of the surface that the first gas bubble had opened upon. The rocket fell steadily, bursting through a third, and then a fourth such bubble. It was clear that the surface of the Moon, at least in that area, was a mass of congealed gas pockets, a honeycomb of thin-walled lava bubbles, perhaps quite deep.

The rocket was almost entirely devoid of its original space momentum by the time it hit the bottom of the last bubble, snapped the thin crust, and fell through it. This time there was a sudden hissing around the battered nose and a warmth began to flow through the body of the rocket. It was enveloped in a belt of hot steam through which it fell several hundred feet and then hit something with a loud splashing noise. The sound vanished as the rocket sank deep into the new substance, came to a halt, and bobbed back upward.

Robin had gotten hold of himself after the third bubble and was hanging on, mentally trying to estimate what had happened. This last sound had been familiar. It must have been water, and the bobbing back of the rocket to the surface confirmed his views. He felt the rocket bounce a couple of times and then subside to a gentle rocking and rolling.

Robin held on for a moment, getting his balance. In some ways the new motion was more disturbing than all that had gone before—the cylindrical body of the rocket, with its blunt end and its rounded nose, was twisting and turning as only can be done by a bottle tossed in a flowing stream. Robin tried to get hold of himself, orient himself to the odd seasick motion, then managed to work his way to the peephole.

He could see nothing. Whatever was outside was without light. But it sounded like water lapping against the sides, it felt like water's forces, and the rocket seemed definitely to be afloat. Robin used his flashlight, tried to direct its beam through the tiny camera outlet. After a little manipulation he succeeded in getting some reflection from outside.

It was water, and the rocket seemed to be floating rapidly along on some sort of dark subterraneous tide. Robin sat back, puzzled. Water—under the Moon?

He held on, still feeling a little dizzy, feeling dirty and itchy, but suddenly beneath it all a little thrilled and pleased. He had survived the crash by some miracle—he was on the Moon and alive! What next?

Next was quick to come. There was a sudden dip in the current and the rocket tilted forward as it shot down a spillway, down a violent decline on a raging torrent, sliding down an unseen waterfall for a surprisingly long time, leveling out at a fast clip, sliding down new tunnels through which the water raced, hitting the side of sharp turns with occasional glancing blows, down more dips and falls, spinning violently around in unseen whirlpools, and finally racing out on a fast stream to gradually slow down and finally come to rest, gently bobbing.

Robin had been knocked around during this breathless ride and only gradually did he realize it was over. Warily he raised his head from where he was sprawled in his tiny closet-compartment and waited. But the gentle bobbing continued.

He put his eye to the peephole and looked. There was a glow outside, a grayish, pale glow, but he could see that the nose of the rocket was somehow grounded on something dry while the tail was still in the water rocking to the current.

He considered his next course of action for a few seconds. It seemed as if he had a chance to escape from his vehicle at last. But escape to what?

Was there air outside, wherever it was that he found himself? If there were air, was it enough to sustain him? Might it not be poisonous or utterly lacking in oxygen?

Well, Robin thought to himself, there isn't really any choice. If I stay here, I'll starve to death or suffocate. If I go out, I may die even sooner. But now or later, if it has to be, it won't make any difference. Whatever the odds in favor of my being able to breathe here, I've got to take them.

He twisted around, found the circular port through which he had originally entered the rocket. He worked at it with his fingers, realizing that it might be quite difficult to open. He worked away the padding that lined the interior, found that it had an arrangement that had automatically sealed it when closed. There was no handle on the inside, for it had never been planned to be opened from that side. However, there were several screws over a small plate, and Robin set to work to unscrew them. He had a Boy Scout knife in his pants pocket—the kind with several blades—and with the back of the biggest blade he worked out the screws.

The panel off, he saw how the sealed gimbals worked, clicked them open and pushed open the door. It held tight for a moment, then popped open. There was a sudden drop in the pressure, Robin's ears popped, and he gasped for breath.

The air outside was lower in pressure than that inside the cargo nose of the rocket, which had been sealed at Earth level. But it was air and it was breathable. Robin drew in several deep lungfuls, savoring it.

It was oddly exhilarating, as if highly charged with oxygen. At the same time there was a smell of mold and dampness and a definite taste of sulfur and phosphorus like that just after a kitchen match has been lighted. Even so, the air was breathable.

Robin worked his head and shoulders through the narrow opening, slid forward and landed on hands and knees on the rocky surface. He got to his feet, looked around.

He was standing on the bank of a rushing stream of water, which was pouring out of a large gap in the side of a cliff. The cliff ran straight up, gently curving to form part of the ceiling several hundred feet overhead. The extent of this ceiling was impossible to determine—it was dark and obscure—but it seemed to Robin almost at once that he was in some sort of gigantic enclosed space—a vast cavern beneath the surface of the Moon, probably several miles beneath it.

The water coming from the underground falls rushed out to form a wide, shallow river which flowed along one side of the cavern and widened out to a few hundred feet clear across to the farther wall. On Robin's side the floor of the cavern rose in a slow slope until it reached its wall perhaps three hundred feet away. Robin could not estimate the length of the cavern. Looking along the river bank, the cave seemed to become veiled in a general mistiness and gathering darkness.

The light itself came from no definite source, but seemed to emanate from the rocky walls and ceiling, from the clayey ground, and from the general atmosphere. Robin supposed that the source was a natural phosphorescence which he knew was not too uncommon even in Terrestrial caverns.

All around on the soil bordering the flowing water was a forest, a forest with the weirdest vegetation Robin had ever seen. Plants growing in clumps and clusters, plants whose large treelike stalks resembled a whitish-blue bamboo, and which burst into globular blue bulbs which seemed to serve as leaves. Among these tree-sized growths was a rich undergrowth of tight balls of varying yellow and green and purple, growing like thick, squat mushrooms. And everywhere else a thick, lush carpet of green, not grasslike but rather like some oversize moss.

In this forest there were no sounds of birds or animals, but only that of plants swaying in the river breeze, the rushing of the waters, and from somewhere distant in the unseen end of the cavern a strange, steady hissing sound.

The rocket, or what was left of it, lay wedged against a section of the bank, its nose up and its tail swaying in the current. Robin looked at it, amazed to find it so small. All that was left of the rocket was the cargo nose, which was the only part sent off after the last of the rocket sections had discharged their forces and been dropped off. The whole affair was not more than about ten feet long, from the battered, blunted red nose, from which several long, straggling orange cords hung—all that was left of the parachute and its attachments—down to the scraped and battered white cylinder that was the cargo compartment. The compartment ended in a flat plate which bore only a few wires that had once connected it with the break-away mechanism of the last of the atomic blasting chambers. This alone was the load of the eight-story tower of energy which had been the Red Sands experimental rocket.

Robin, without further delay, bent down to the cylinder and began to haul and push it entirely out of the water to the dry ground. He knew he could not afford to risk its loss. To his surprise, moving the rocket head was an easy task. It was extremely light and he found himself possessed of tremendous strength, tired and bruised and sore as he was.

It was, he thought, as he pulled the rocket along, the Moon and its weak gravity. He would only weigh a sixth of his Earth weight here, so would the cargo head, yet he would have the muscles necessary for much more than that weight. He would literally be a superman here—if he could survive.

Survival, he knew, would be the question. He didn't know whether even now he might be inhaling poison from the strange, thin sublunar air. He didn't know what mysterious radioactive rays might be bathing him with their baleful influence. He didn't know whether any of the vegetation in this cavern world would be edible.

Having brought the cargo cylinder to a safe spot many feet from the water, Robin looked for the door that would open the animal compartment. He found it, forced it open. Inside were the two cages. Gently he reached in, unscrewed them from their holdings, and lifted them out.

One of the monkeys was dead, probably killed by some of the jouncing the rocket had taken. The other, looking miserable, was clinging to the bars chattering. Robin looked at it, and the monkey looked back. The young man unlatched the cage, reached in, and took the little brown animal by the back of the neck. But the monkey made no effort to bite. Instead, it twisted around, grabbed Robin's arm, and hung tight.

When his grip was released, the monkey scurried up Robin's arm and clung to his shoulder, recognizing the need for companionship after its frightening experiences.

The rabbits had fared slightly better. One of them was dead, but the other three, while somewhat beaten around, were alive and sniffling their pink noses. Robin saw that there was very little food or water left for the animals.

Here then was the means to test the Moon's capacity to produce food and drink. First, however, Robin decided he would build a pen for the rabbits. If he were lucky, he could breed them and have at least one source of food suited to his system.

He went over to the nearest clump of ball-trees, looked them over, tested his strength on them. They broke easily and quickly when he grasped one by the trunk and pulled. He found that it could be splintered into shreds fairly rapidly and that inside the shell of the stalk was a mass of cottony matter.

He shredded a number of the stalks, and then staked them out in the ground to make a small fenced pen, tying the whole together with one of the long cords hanging from the parachute nose. Into this makeshift pen, he released the three rabbits. He filled the cup from their cage with water from the river, placed it in the pen. The rabbits hopped over, sniffed, and drank. They seemed to suffer no ill effects.

Robin broke open one of the ball-like growths from the tree, found it contained a substance resembling a combination of melon and potato. He offered some of this to the rabbits and after an interval they ate it and seemed to like it.

The monkey was chattering away as Robin did this and suddenly scampered down and snatched a piece of the ball-food, stuffing it into its mouth. Robin had not wanted to use the little creature for a test but the damage was done. However, the monkey seemed to enjoy it.

Robin sat down on the ground and watched. He felt tired, now realized just how tired he was, how sorely he ached from his experience. He felt warm and headachy now that the strain was over. He knew he still had things to do. He wanted to try to make a fire and cook the rabbit that had been killed. He was thirsty as well. He wanted to tie a cord to the monkey so that the animal would not run away into the unknown and possibly dangerous regions of the cavern. He wanted to find a safe place to sleep and hide should there be some sort of animal life around.

But he was growing terribly sleepy and feeling quite sick. He curled up, and before he could stop himself, he was asleep.

The rabbits nibbled on. The monkey sat on a ball in one of the strange trees and watched in silence. Far off, somewhere in the cavern, the mysterious hissing continued.