The odd tingle came and vanished. "Now!" Wells roared, and Brown leaped down the thin steel rungs.

He staggered at the bottom from the force of his impact, then straightened and raced madly forward. Through the drone of the motors the two officers could hear the staccato beat of his feet.

But their eyes were glued to the teleview. Through clutching beds of seaweed the enemy submarine was ploughing. Her great, smooth bow lay straight ahead, metal hawser arm spanning the thirty feet between them. In another second, Keith thought grimly, two dynamite packed tubes of sudden death would thunderbolt into that hull, and--

Brown pulled the lever.

The tubes spat out compressed air; a scream ran through the submarine; and the two steel fish leaped from their sheaths, their tiny props roaring. Over the narrow gulf they shot; the range was short, their target dead ahead--and yet by bare inches they missed!

No answering roar bellowed back. Keith had watched their course; had seen them flash by the enemy's bow, flicking it with their rudders, but nothing more. "Why?" he cried. And, as Bowman moved his hands in a hopeless gesture, he saw in the teleview the reason.

It was a jagged pinnacle of rock, which, just before Brown had fired, had been straight ahead. The towing monster had seen it and veered sharply to avoid crashing. The barest change of course, yet sufficient to avoid the torpedoes....

Wells and Bowman were cursing savagely when the sound of Brown, racing desperately aft, jerked the commander to the ladder. He saw the petty officer at its foot. "Hurry!" Wells shouted. "The ray!"

Brown grasped the steel rungs and scrambled upward, but he was too late. The fatal charge tingled. A peculiar, surprised expression washed over his face; his hands loosened their grip. For a second his eyes looked questioningly at his commander; a faint sigh escaped him; and then his arms flung out, his body relaxed, and he slumped like a slab of meat to the deck below....

Keith Wells saw red. Blind to everything, he was just about to charge down the ladder to himself re-load the forward tubes when the grip of Hemmy Bowman's hand stayed him. The thing Hemmy was staring at in the teleview screen sobered him completely.

The wall of rock to which the enemy submarine had first been charging had become visible, soaring vastly from the gloom of the sea-floor.

And the monster was towing them straight into a dark, jagged cleft at its base.

"It's a cavern!" Keith breathed. "A split in the rock--the lair of that devil. And we're being dragged into it!"

CHAPTER III

_Sacrifice_

At that moment Keith Wells knew fear. Each second they were being hauled closer to the monster's dim lair. It lay there, dark, mysterious, fingered by gently swaying, clammy kelp. A hushed solitude seemed to reign over it, aweing all undersea life from the vicinity.... Wells turned his head to meet Bowman's eyes, and read in them a silent question.

What now?

He groaned in the agony of his mind. In a few minutes, all would be over. Once the _NX-1_ was dragged into that dark cavern there'd be no chance of escaping to warn the world above, of saving the submarine.

What now? The question brought beads of sweat to his tormented brow.

He, Keith Wells, standing impotently by while his ship, the pride of the service, was hauled inch by inch to some strange doom!

Racked by these thoughts, he murmured tortured, jerky phrases, unconscious he was giving voice to the things that flogged his brain.

"What can I do? I've got to save my ship--I've got to get back to break the news--I've got to tell the world! But how? How--" His expression changed suddenly. "That's it! That hawser arm between us must be broken!"

"Yes."

First Officer Hemingway Bowman's clear voice broke in on the older man's thoughts with that one crisp word. Keith swung to find the other's eyes fixed levelly on his.

"You're right, Keith. The hawser arm must be broken; with a depth charge, of course. It's the only way.

"To attach a depth charge," he continued evenly, "a man must leave the ship. You can't, Keith. It will be me."

The commander did not speak. "I'll put on a sea-suit," Hemmy went on quickly, eyes lighting. "You tip the submarine and I'll slide out the conning tower exit port on the lee side, so they can't see me, and worm forward through the kelp. We're almost holding them even; that'll be easy. I'll be protected from the paralyzing shock until the last second, and it may not get me outside; that'll have to be chanced. The hawser arm's only some ten feet above the sea-floor; I can reach it with a hook on the charge." He paused.

"I'll attach it; and when it bursts I'll try to get back and grab that ring on the midships exit port, and you can let me in when we get to the surface. But if I take too long, Keith--if I miss--you beat it without me. You understand? Beat it!"

He gazed straight at his friend. "Understand, Keith?"

Commander Keith Wells bowed his head in acquiescence. He was afraid that if he met Hemmy Bowman's steady eyes he'd make a fool of himself....

Hemmy glanced at the screen once more, shivering as he saw how near the black cavern was. Then he moved rapidly, playing the cards carefully for his gamble with death. He had to: the trumps were in the other hand.

From the locker where their sea-suits were stowed he grabbed his own, and with quick fingers ripped the slides and fitted it on. A sheath of yellow Lestofabrik, its weighted feet and gleaming casque transformed his slim figure into a giant such as might stalk through a nightmare.

Built cunningly into the helmet was a tiny radio transmitter and receiver, with a range of a quarter-mile; hugging to the shoulders, inside nestled the air-making mechanism, its tiny generators already in motion. Around the helmet was fastened a small removable undersea-light. The wrists of the suit were very flexible, permitting the freest motion.

Once in the suit, Hemmy smiled through the still-opened face-shield.

"Got the depth charge ready, Keith? Make it fast--that cavern's near!... Good!"

Silently the commander fitted the black bomb to his friend's shoulders. It was timed to fire a minute after being set. A long wire hook craned from its top, and this hook Bowman would fasten on the hawser arm.

"Without Sparks, I guess I'll have to communicate with you through portable," Keith said, and quickly donned one of the tiny portable sets.

"Right. Ready, Keith."

Bowman started his awkward, crawling progress up the ladder into the conning tower just above, Keith helping from behind. When they stood before the exit port on the lee side, Wells shot back its bolts and the door swung open, revealing the black emptiness of the water chamber. The commander gazed for a second into Bowman's eyes. The moment had come.

Keith turned his head away, felt a hand grip his. He wrung it tightly....

Bowman clumped into the chamber.

The commander closed and locked the door, and he heard the streaming water pour in as Hemmy turned the valve. Then Wells sped down the ladder and tilted the diving and course rudders of the submarine.

She swayed daintily over to port; held there. A moment later the recurring electric tingle brushed him. Had the enemy seen Bowman leave? Had the ray struck him down?

He glared into the teleview. "Thank G.o.d!" he breathed. For Hemmy had already slid down the _NX-1's_ smooth hull and was safe on the sea-floor beside her.

"Everything right?" Wells asked, speaking into the microphone of his portable.

"All O.K.," came the answer. "Going forward now. Kelp thick as h.e.l.l."

Keith's eyes bored at the screen. This misshapen monster who was his friend! Almost obscured by bands of thick-leaved kelp the yellow form moved, hands clearing a pathway through the weeds. Slowly but surely he made for the bow of the submersible.