They were afloat, and comparatively safe from the rockets which shrieked out of the leaden sky and threw spectral waterspouts up into the fog before they exploded. Unless one exploded directly under them, or very near, they would be safe—for the time being.

"Which way is shore?" Lents puffed.

"Rockets seem to come from that way," Sine answered, flipping his hand. "Swim that way. Fish probably lost appetites, so won't bother us."

The bombardment had indeed frightened away the monsters of the deep, and even the dead in the ruined submarine city would rest in peace for a while. But the Earthmen, after several hours of swimming, doubted that this was more than a postponement of death. The long greasy swells were rising, presaging another of Jupiter's unimaginably violent storms.

"I see a light!" Sine strained his eyes to get another glimpse of it through the brown fog. "There it is again." Something was moving slowly through the air a short distance over the water, following the course of the rockets, which had ceased coming. A powerful searchlight was cutting through the murk. A war party of the First Race, looking for wreckage.

In their methodical search they soon found the swimming men, and they were helped into the chief's cabin. Sine, looking up with half-blinded eyes, saw Governor Nikkia sitting in his chair, looking at him coldly.

"So!" the governor bit off his words. "The traitors are fished out." His arrogant, handsome face was vindictive, uncompromising. "We forgot that the aborigines of Earth would naturally sympathize with their equals, the Mugs! That was nicely timed, your 'visit.' How long have you been in communication with the rebels?"

The Earthmen, weak and exhausted by their long exposure, resisted their desire to lie down on the floor. They stood before the governor, hemmed in by hostile fighting men, and tried to maintain the traditions and dignity of their planet.

"We were not in communication with your slaves," Sine declared. "You should know that. Your radio monitors would have picked up any messages, and your own patrol ships picked us up when we were far out in space. Our mission is one of peace. As for your quarrels, they do not concern us. We are strictly neutral."

Nikkia laughed, a short, clipped bark in which there was little amusement.

"Well, your guilt is a matter of small moment anyway. We have paid the Mugs for the damage they did, and they will not have another chance. And if they had an idea of getting help from Earth, you shall be an object lesson on the uselessness of such hopes."

"Meaning?" But Sine and his companions knew that the meaning must be evil.

"Meaning," Nikkia snapped, "that from now on you three are Mugs, no better and no worse than the Jovian Mugs. Except that I shall instruct the labor office to put you to work at one of the power integrators—perhaps in The Bubble. We don't want to waste you" he added with grim humor—"and the gravity here on Jupiter might reduce your life of usefulness."

The governor turned his back in dismissal, and the prisoners were hustled into a dark, extremely hot storage hold. Here they lay down amid an untidy collection of miscellaneous gear, thick with dust. They rested gratefully until some of their strength should return to them.

When they awoke from their sleep of exhaustion they were aware that the ship had landed, and a few minutes later the door of their prison was opened and an officer, heat pistol trained on them, commanded the prisoners to get into another ship for transfer to the metal and crystal satellite where they were condemned to drag out the rest of their lives as slaves.

The second coming of the Earthmen to The Bubble was in marked contrast to their first. Instead of the large, commodious lock in the upper hemisphere, they entered this time through a drab, dull orifice in the black half of the sphere. The patrol ship which brought them was contacted without ceremony. They were thrust though with curt orders to ask somebody for the Mug superintendent's office. Then the valve closed behind them. There was a grating sound as it was locked from the outside, and then silence. The ship was gone. They were marooned in the gloom, the grisly domain of the rays and the Mugs. Sentenced for life, with their only companions, a few broken, despairing men.

The corridor in which they found themselves sloped gently downward, and artificial gravity made it possible to walk naturally. Sine taking the lead, they passed into the depths. Everywhere were monstrous shadows, with occasional stabbing eerie beams of light. But it seemed that an ominous hush hung over this metal-interlaced gulf. Here there was no sense of motion—no sense of bubble-like lightness. It was like a descent into the nether regions of the ancient—into an inferno. But of the denizens of this dismal place there was no trace.

"Let's go to Proserpina's home," Sine suggested. "I'm anxious to see if she's still all right. And the old man too."

Accordingly they watched for the numbered corridor, and after some fruitless wandering, came again to the deep crack that was the only home this timid girl knew. She started up in terror as the Earthmen came into view. Not unnaturally, for they were all bristly with unshaven beards and grimy with the dust they had collected when prisoners in the Jovian ship's hold.

But after her first reaction of terror she gave a glad cry, and running up to Sine, threw her thin arms around his muscular neck.

"Now listen, kid!" The young scientist began with unwonted embarrassment. But the girl clung to him, and he could not quite bring himself to tear her arms away. She released him herself, in a few moments, became suddenly shy.

Lents laughed with genuine amusement.

"Don't be silly, Sine. She's just glad to see us again. Poor kid was lonesome. Come here, Prosie."

She went to him, gravely embraced him; then Kass.

They noticed she was trembling.

"What's the matter?" Kass asked. "You act as if you're glad to see us, but wished we hadn't come."

"Why are you here?" she asked with a troubled frown.

The Earthmen told her of what had transpired—that they were now condemned for life to serve in the dark hemisphere. As they spoke her fears seemed to vanish. She became radiant with delight.

"Then you have come at the right time!" she cried. "Our slavery is at an end, and you shall pilot us back to the Mother planet!"

"You're not crazy, are you kid?" Sine asked, lifting her little pointed chin with his hand.

"No!" she laughed delightfully. "Not crazy!" And she would have embraced Sine again. "My father has been building a ship for the past two years, hoping to escape to Ganymede, or some other moon of Jupiter. But now we shall go to Earth!" She clapped her hands excitedly.

"Listen! Let's get this straight," Lents demanded. "You say your dad has built a ship. Where is it?"

"Way down in the bottom of the hemisphere. That's where all the Mugs are, working on it when they have time. Dad's chest feels better again."

"They have built a ship, huh?" Sine was trying to suppress the hope that flamed up madly. "How'll they get it out?"

"They've made an airlock, so that when we leave the escaping air won't give us away."

It was one of these things that seem too good to be true. But when the Earthmen accompanied the girl to the secret workshop, directly next to the sphere's outer skin, they found she had spoken the truth in every respect. The men there, nearly all pathetic wrecks of the First Race's system, were at first a little doubtful about admitting the Earthmen, but one after another they were won over to the idea of seeking sanctuary on Earth rather than on some satellite of Jupiter where they would never be entirely safe. Besides, the Earthmen, though they had been stripped of all their weapons, represented additional fighting strength.

They made their final preparations with mixed feelings. Many of the Mugs had relatives on Jupiter, though few had wives or children. Even women of the Second Race had no desire to share the fate of a man condemned to a lifetime in the black half of the Bubble. Those few women who had accompanied their men to the metal satellite would, of course, be taken along, for the escape ship was commodious.

The next two weeks were filled with arduous labor, but at last the ship was ready, and observation through a small port which had been installed, showed that they were about to enter the shadow of Jupiter. Under cover of darkness they would leave the airlock. They would accelerate past The Bubble. Centrifugal force would send them away from Jupiter. At the same time their velocity with relation to the sun would be diminished. Lents plotted a long, graceful curve that would bring them to Earth with the best possible speed.

Proserpina's father lay on the floor, peering out through the port.

"Remember, Jan," Lents reminded him, "as soon as we cut the shadow, you give the order." They were all in the ship save the Earthmen and Jan, lying on the floor like a great spider, with his tremendous chest laboring painfully.

"In a moment now," Jan said. "The sun is nearing the limb."

"Open! Open, you aberrated spores!" The command came but faintly through the inside valve of the emergency airlock.

"They've found out!" Kass gasped. "Quick, never mind the shadow!"

Jan had already leaped to the long cylindrical hull, the product of endless labor and sacrifice.

"Inside!" Sine shouted. Kass and Sine made for the ship's manports. "I'll take care of the thermite."

In his hand he carried a small heat pistol that had long ago been stolen and hidden by a Mug. Quickly he made a circuit of the room, which was like an enormous sheet-metal blister on the inside of the metal satellite. After the thermite had cut out the ship free, that blister would prevent the escape of air, saving the lives of thousands of the First Race and also preventing discovery of their escape for a time.

The thermite was piled generously in a ridge all the way around. Sine leaped inside the first valve of the manport, colliding with a soft body.

"Get inside, kid!" He leveled his pistol at the thermite ridge where it was nearest to him. High time too. The walls of the blister were radiating heat. The fools were turning their infra-red beams on it!

"Lock!" Sine shouted, pressing the trigger and jumping back.

Instantly the ship was surrounded by an oval of brilliant orange and white fire. The valve clicked shut in Sine's face, and he dived through the second one into the interior, tripping the lock of that one also.

Through the ports nothing was to be seen now save fire. They were in an inferno of brilliant light and heat. But through the glare and smoke Sine saw a white-hot spot suddenly appear on the blister wall. The Jovians were melting their way through! The metal plates sagged like wet paper, dropped limply. Back of the hole, luridly illuminated, stood the foremost of a detachment of fighting men, eager to leap to the fray, waiting only for the metal to cool a little.

But the thermite had been burning steadily, biting through the tough skin of the metal moon. Just as the fugitives were beginning to wonder whether they would be incinerated in their self-made prison there was a lurch. Through the hull of their own vessel they could hear the tearing of metal as the weakened plates were sheared away. They found themselves in space, with the great ball of the Pleasure Bubble floating away from them. Just outside of the gaping hole in the sphere floated the bodies of twenty or thirty men, blown out by the escaping air.

The air was escaping in a prodigious geyser; unimpeded by an atmosphere, it spewed out, visible like a cloud due to its moisture, smooth like an inflating balloon without billows. The ball of vapor expanded swiftly toward the gray vastness of Jupiter 100,000 miles below, enveloping the fugitive ship for a time, then passing on, like an enormous milky white cloud, falling swiftly until it was lost in the darkness, still expanding.

Overhead The Bubble continued serenely on its course, the sweeping curve of its crystal hemisphere visible. But now the actinic lights that had served as artificial suns were dark. The great man-made paradise was as cold and dead as the Earth's moon. Death stalked its pleasure palaces. Already up there the pleasant rippling lakes must be skimmed over with ice, the luxuriant vegetation stiff, crackling with frost.

Despite the selfishness, the cruelty, the utter callousness of the First Race, Sine felt a pang of regret over the destruction of so much beauty.

A messenger from the astrogator's cabin, a man whose skin was seared and scorched so that it looked like an alligator's hide, touched Lents' arm.

"Jan would like to have you verify the course." There was apprehension in the man's voice. Member of a race so long enslaved, restrained, he feared the freedom of open space.

They swept slowly past The Bubble, gaining speed. Suddenly there was a cry from the stern look-out:

"The ship's heating. Stop it! Something's wrong."

Sine, rushing to answer the call, found that the ship was indeed heating up. Shielded from the sun's rays as they were, this was inexplicable. And then he saw the dull red pinpoint of light.

He had not seen it before, that patrol ship, clinging like a leech to the airlock of the crystal hemisphere. There had been men in there when the air escaped. They had been saved from death by the closing of their automatic airlocks.

"Better get back into the shelter of The Bubble," he told Jan after a hurried trip to the astrogator's cabin. The spider man turned the vessel, and they scurried back to shelter. Although the patrol ship tried its gravity buttons on them, the Mugs had fully equipped their own vessel with similar, and larger buttons which were occasionally used in regulating the metal satellite's orbit. They could neutralize the other vessel's gravity force with ease.

"And yet," Sine admitted to the serious little group in the cabin, as they once more floated in space under the immense sphere, "they seem to have us stymied."

"Suppose they follow us around here?" Kass asked somewhat nervously.

"I don't think they can," Sine said. "I noticed when we came to The Bubble first, the ships are locked to the gaskets from inside the sphere. The men inside the ship can not unlock their ship unless they open the emergency air curtain. If they did their air would all escape through the sphere. They could do it, of course, if they put on space suits. But that procedure would take an hour, and in the mean time we could get out of range of their heat rays. So we have them stymied too. Except for one thing——"

"Of course," Lents grunted. "We can't get at them, and they can't get at us, but in a few hours we'll be in sunlight again, and some patrol will pick us up."

The Mugs, watching fearfully from beyond the doorway, turned aside. Were they, after a mere glimpse of freedom, to be immediately returned to the bondage which had become unbearable to them? Sine felt a small, thin hand slip into his. He looked down into the wistful face of Proserpina looking up at him with hope, with confidence. All at once his shyness vanished as he realized that Proserpina's obvious adoration for him was only the admiration of a child for a very big and very wonderful brother. At the same time his desire to do something to release them all from their peril was intensified by the imperatively felt need to justify her confidence in him. An idea came.

"Jan," he asked. "What is the energy output—the total capacity—of our gravity buttons?"

Jan named an approximate figure in ergs.

"Lents, if you've ever calculated to a purpose, calculate now! How much energy is represented by the mass of that sphere at its orbital velocity?"

"I get you!" The fat scientist puffed out his cheeks with excitement. "Have to estimate the mass first." He picked up a stylus from the astrogator's table, worked furiously on a tablet. Kass and Jan watched apprehensively. The Pleasure Bubble, with its freight of the dead, was hurrying remorselessly to its rendezvous with the sunlight.

"Whoops!" Lents threw his tablet into the air in extravagant triumph. "She'll do!"

"Stations!" shouted Jan, in his curious strained voice, and men rushed eagerly to their posts, still hazy as to their object but cheered by the knowledge that there was hope after all.

Then began one of the strangest duels in the history of the solar system. Setting the nose of their vessel against the gigantic metal satellite, they directed the stern gravity buttons against a distant star, and applied full force to slow the sphere in its orbit.

The forces liberated were terrific. The sphere's tough skin, three inches thick, buckled and bent inward until the ship was almost buried in a pit of its own creation. Jan stood hunched over the activator lever like a great spider, ready to throw it into neutral at the first sign of an actual rupture, which would send them crashing through the internal cells and girders of the sphere.

"She's folding up like a squeezed orange peeling!" Kass muttered, running his hand over his bald head.

"Built to withstand internal pressure—nothing like this," Jan gasped. "Stout ship, this!" he added a moment later. "We thought we might have to ram our way out."

She was indeed a stout ship—this vessel of escape. Though she shivered and groaned, she gave no indication of failure.

"Wonder if the others are pushing against us!" Kass suddenly thought of another possibility.

"We—can—outpush 'em." Jan gasped. "Got to sit down. Here you take it!" Sine stepped into his place. Vague shocks and noises were transmitted to them through the hull. The huge sphere was collapsing progressively.

Lents came puffing from an observation port.

"She's slowing!" he reported triumphantly. "Our trajectory—give her a little more!"

The Joy Bubble was becoming more and more disc-shaped, and it was slowly turning on a major axis as the contending forces became uncentered.

"Flopping like a flapjack," Lents commented as he watched the shifting vista. A moment later; "It's a close squeeze. See there, past the horizon—a prominence?"

It was like a white plume, this jet of vapor thrown far into space. Not uncommon in Jupiter's turbulent atmosphere. But it was bright, dazzling! That meant they were not far from the sunlight!

"Pull away!" the fat mathematician shouted. "We have to take a chance!" Instantly Sine reversed the lever. Everyone grasped handholds as the ship backed out of the pit. Now they could see the vast ruin they had wrought. Sine gave her all the speed he dared, for the sun, for home!

The great ruin was slowly turning, and in a few minutes they saw again the darker shadow that was the fighting patrol ship, still clamped to her side. At the same instant the dull red pinpoint winked on. The Jovians had sighted them again! In a few minutes the hull was getting uncomfortably warm.

Lents laid down his pad.

"They will crash!" he declared. "But they have an hour, the fools! Instead of trying to burn us why don't they get into their space suits and free themselves?"

Jan, resting on the bench, shook his shaggy head.

"They are a great people, stupid but great. They will try to punish us till they die."

The wreckage drifted closer and closer to Jupiter, and still the red beam played steadily on the fleeing prisoners' ship. The distance had become so great that it could only be seen through an old telescope that the prisoners had somehow procured. But the prisoners were gasping. Their hull was cherry-red on the outside, and still heating. A few more minutes and the heat would be unbearable.

"They are getting closer—closer—they are in the sunlight. Now I can see better. I believe they will skip by—no! They've dived into the vapor! They're out again. Skipped out like a flat stone on water. Sinking again—almost over the horizon. Gone, I guess. Whew, it's hot!"

They were accelerating so fast that they had to turn on the interior gravity buttons to equalize the pressure on their bodies. Behind lay the vast, fog-bound planet of Jupiter. Ahead was the beautiful sun. And somewhere beyond, and still invisible, Earth the lovely, the green, the Mother of the human race!

THE END