Since both Costigan and Bradley had often watched their captors at work during the long voyage from the Solar System to Nevia, they were quite familiar with the machine tools of the amphibians. Their stolen lifeboat, being an emergency craft, of course carried full repair equipment; and to such good purpose did the two officers labor that even before their air-tanks were fully charged, all the damage had been repaired.

The lifeboat lay motionless upon the mirror-smooth surface of the ocean. Captain Bradley had opened the upper port and the three stood in the opening, gazing in silence toward the incredibly distant horizon, while powerful pumps were forcing the last possible ounces of air into the practically unbreakable storage cylinders. Mile upon strangely flat mile stretched that waveless, unbroken expanse of water, merging finally into the violent redness of the Nevian sky. The sun was setting; a vast ball of purple flame dropping rapidly toward the horizon. Darkness came suddenly as that seething ball disappeared, and the air became bitterly cold, in sharp contrast to the pleasant warmth of a moment before. And as suddenly clouds appeared in blackly banked masses and a cold, driving rain began to beat down in torrents.

"Br-r-r, it's cold! Let's go in--Oh! Shut the door!" Clio shrieked, and leaped wildly down into the compartment below, out of Costigan's way, for he and Bradley also had seen slithering toward them the frightful arm of the Thing.

Almost before the girl had spoken Costigan had leaped to the levers, and not an instant too soon; for the tip of that horrible tentacle flashed into the rapidly narrowing crack just before the door clanged shut. As the powerful toggles forced the heavy screw threads into engagement and drove the massive disk home into its bottle-tight, insulated seat, that grisly tip fell severed to the floor of the compartment and lay there, twitching and writhing with a loathsome and unearthly vigor. Two feet long the piece was, and larger than a strong man's leg. It was armed with spiked and jointed metallic scales, and instead of sucking disks it was equipped with a series of mouths--mouths filled with sharp metallic teeth which gnashed and ground together furiously, even though sundered from the horrible organism which they were designed to feed.

The little submarine shuddered in every plate and member as monstrous coils encircled her and tightened inexorably in terrific, rippling surges eloquent of mastodonic power; and a strident vibration smote sickeningly upon Terrestrial eardrums as the metal spikes of the monstrosity crunched and ground upon the outer plating of their small vessel. Costigan stood unmoved at the plate, watching intently; hands ready upon the controls. Due to the artificial gravity of the lifeboat it seemed perfectly stationary to its occupants. Only the weird gyrations of the pictures upon the lookout screens showed that the craft was being shaken and thrown about like a rat in the jaws of a terrier; only the gauges revealed that they were almost a mile below the surface of the ocean already, and were still going downward at an appalling rate. Finally Clio could stand no more.

"Aren't you going to do something, Conway?" she cried.

"Not unless I have to," he replied, composedly. "I don't believe that he can really hurt us, and if I use a ray of any kind I'm afraid that it will kick up enough disturbance to bring Nerado down on us like a hawk after a chicken. However, if he takes us much deeper I'll have to go to work on him. We're getting down pretty close to our limit, and the bottom's a long way down yet."

Deeper and deeper the lifeboat was dragged by its dreadful opponent, whose spiked teeth still tore savagely at the tough outer plating of the craft until Costigan reluctantly threw in his power switches. Against the full propellant thrust the monster could draw them no lower, but neither could the lifeboat make any headway toward the surface. The Terrestrial then turned on his rays, but found that they were ineffective. So closely was the creature wrapped around the submarine that his weapons could not be brought to bear upon it without melting the vessel's own outer skin.

"What can it possibly be, anyway, and what can we do about it?" Clio asked.

"I thought at first it was something like a devilfish, or possibly an overgrown starfish, but it's too flat, and has no body that I can see," Costigan made answer. "It must be a kind of flat worm. That doesn't sound reasonable--the thing must be all of a hundred meters long--but there it is. The only thing left to do now, as I see it, is to try to boil him alive."

He closed other circuits, diffusing a terrific beam of pure heat, and the water all about them burst into furious clouds of steam. The boat leaped upward as the metallic fins of the gigantic worm fanned vapor instead of water, but the creature neither released its hold nor ceased its relentlessly grinding attack. Minute after minute went by, but finally the worm dropped limply away--cooked through and through; vanquished only by death.

"Now we've put our foot in it, clear to the knee!" Costigan exclaimed, as he shot the lifeboat upward at its maximum power. "Look at that! I knew that Nerado could trace us, but I didn't have any idea that they could. It's a good thing these ultra-vision plates don't need light to see by or we'd be 'spurlos versenkt' in a hurry!"

Staring with Costigan into the plate, Bradley and the girl saw, not the Nevian sky-rover they had expected, but a fast submarine cruiser, manned by the frightful fishes of the greater deeps. It was coming directly toward the lifeboat, and even as Costigan hurled the little vessel off at an angle and then upward into the air one of the deadly offensive rods, tipped with its glowing ball of pure destruction, flashed through the spot where they would have been had they held their former course.

But powerful as were the propellant forces and fiercely though Costigan applied them, the denizens of the deep clamped a tractor ray upon the flying vessel before it had gained a mile of altitude. Costigan aligned his every driving projector as his vessel came to an abrupt halt in the invisible grip of the beam, then experimented with various dials.

"There ought to be some way of cutting that beam," he pondered audibly, "but I don't know enough about their system to do it, and I'm afraid to monkey around with things too much, because I might accidentally release the screens we've already got out, and they're stopping altogether too much stuff for us to do without them right now."

He frowned as he studied the flaring defensive screens, now radiating an incandescent violet under the concentration of the forces being hurled against them by the warlike fishes, then stiffened suddenly.

"I thought so--they can shoot 'em!" he exclaimed, throwing the lifeboat into a furious corkscrew turn, and the very air blazed into flaming splendor as a dazzlingly scintillating ball of energy sped past them and high into the air beyond.

Then for minutes a spectacular battle raged. The twisting, turning, leaping airship, small as she was agile, kept on eluding the explosive projectiles of the fishes, and her screens neutralized and re-radiated the full power of the attacking beams. More--since Costigan did not need to think of sparing his iron, the ocean around the great submarine began furiously to boil under the full-driven offensive beams of the tiny Nevian ship. But escape Costigan could not. He could not cut that tractor beam and the utmost power of his drivers could not wrest the lifeboat from its tenacious clutch. And slowly but inexorably the ship of space was being drawn downward toward the ship of ocean's depths. Downward, in spite of the utmost possible effort of every projector and penetrator, and the two Terrestrial spectators, sick at heart, looked once at each other. Then they looked at Costigan, who, jaw hard set and eyes unflinchingly upon his plate, was concentrating his attack upon one turret of the green monster as they settled lower and lower.

"If this is ... if our number is going up, Conway," Clio began, unsteadily.

"Not yet, it isn't!" he snapped. "Keep a stiff upper lip, girl. We're still breathing air, and the battle's not over yet!"

Nor was it; but it was not Costigan's efforts, mighty though they were, that ended the attack of the fishes of the greater deeps. The tractor beam snapped without warning, and so prodigious were the forces being exerted by the lifeboat that, as it hurled itself away, the three passengers were thrown violently to the floor, in spite of the powerful gravity controls. Scrambling up on hands and knees, bracing himself as best he could against the terrific forces, Costigan managed finally to force a hand up to his panel. He was barely in time; for even as he cut the driving power to its normal value the outer shell of the lifeboat was blazing at white heat from the friction of the atmosphere through which it had been tearing with such an insane acceleration!

"Oh, I see--Nerado to the rescue," Costigan commented, after a glance into the plate. "I hope that those fish blow him clear out of the Galaxy!"

"Why?" demanded Clio. "I should think that you'd...."

"Think again," he advised her. "The worse Nerado gets licked the better for us. I don't really expect that, but if they can keep him busy long enough, we can get far enough away so that he won't bother about us any more."

As the lifeboat tore upward through the air at the highest permissible atmospheric velocity Bradley and Clio peered over Costigan's shoulders into the plate, watching in absorbed interest the scene which was being kept in focus upon it. The Nevian ship of space was plunging downward in a long, slanting dive, her terrific beams of force screaming out ahead of her. The rays of the little lifeboat had boiled the waters of the ocean; those of the parent craft seemed literally to blast them out of existence. All about the green submarine there had been volumes of furiously-boiling water and dense clouds of vapor; now water and fog alike disappeared, converted into transparent superheated steam by the blasts of Nevian energy. Through that tenuous gas the enormous mass of the submarine fell like a plummet, her defensive screens flaming an almost invisible violet, her every offensive weapon vomiting forth solid and vibratory destruction toward the Nevian cruiser so high in the angry, scarlet heavens.

For miles the submarine dropped, until the frightful pressure of the depth drove water into Nerado's beam faster than his forces could volatilize it. Then in that seething funnel there was waged desperate conflict. At that funnel's wildly turbulent bottom lay the submarine, now apparently trying to escape, but held fast by the tractor rays of the space-ship; at its top, smothered almost to the point of invisibility by billowing masses of steam, hung poised the Nevian cruiser.

As the atmosphere had grown thinner and thinner with increasing altitude Costigan had regulated his velocity accordingly, keeping the outer shell of the vessel at the highest temperature consistent with safety. Now beyond measurable atmospheric pressure, the shell cooled rapidly and he applied full touring acceleration. At an appalling and constantly increasing speed the miniature space-ship shot away from the strange, red planet; and smaller and smaller upon the plate became its picture. Long since the great vessel of the void had plunged beneath the surface of the sea, more closely to come to grips with the vessel of the fishes; for a long time nothing of the battle had been visible save immense clouds of steam, blanketing hundreds of square miles of the ocean's surface. But just before the picture became too small to reveal details a few tiny dark spots appeared above the banks of cloud, now brilliantly illuminated by the rays of the rising sun--dots which might have been fragments of either vessel, blown bodily from the depths of the ocean and, riven asunder, hurled high into the air by the incredible forces at the command of the other.

Nevia a tiny moon and the fierce blue sun rapidly growing smaller in the distance, Costigan swung his visiray beam into the line of travel and turned to his companions.

"Well, we're off," he said, scowling. "I hope it was Nerado that got blown up back there, but I'm afraid it wasn't. He whipped two of those submarines that we know of, and probably half their fleet besides. There's no particular reason why that one should be able to take him, so it's my idea that we should get ready for great gobs of trouble.

"They'll chase us, of course; and I'm afraid that with their immense power, they'll catch us."

"But what can we do, Conway?" asked Clio.

"Several things," he grinned. "I managed to get quite a lot of dope on that paralyzing ray and some of their other stuff, and we can install the necessary equipment in our suits easily enough."

They removed their armor, and Costigan explained in detail the changes which must be made in the Triplanetary field generators. All three set vigorously to work--the two officers deftly and surely; Clio uncertainly and with many questions, but with undaunted spirit. Finally, having done all they could do to strengthen their position, they settled down to the watchful routine of the flight, with every possible instrument set to detect any sign of the pursuit they so feared.