"No, only a little absent-minded," I replied. Then, "Come on, Stanley.

We'll round up every able bodied citizen in Zyobor and get to work. I suppose they have some kind of rock drilling machinery here?"

They had. And they strangely resembled our own rock drills: revolving metal shafts, driven by gas turbines, tipped with fragments of the same crystal that glittered so profusely in the palace walls. Another proof that practically every basic, badly needed tool had been invented again and again, in all lands and times, as the necessity for it arose.

With hundreds of the powerful men of Zyobor working as closely together as they could without cramping each others movements, and with the whole city resounding to the roar of the machinery, we labored at the defence that might possibly check the advance of the hideous Quabos.

And with every breath we drew, waking or sleeping, we realized that the cold blooded, inhuman invaders had crept a fraction of an inch closer in their tunneling.

The Quabos against the Zyobites! Fish against man! Two diametrically opposed species of life in a struggle to the death! Which of us would survive?

The hour of the struggle approached. Every soul in Zyobor moved in a daze, with strained face and fear haunted eyes. Their proficiency in mental telepathy was a curse to them now: every one carried constantly, transmitted from the brains of the servant-fish outposts, a thought picture of that outer cavern in the murky depths of which writhed the thousands of crowding Quabos. Each mind in Zyobor was in continual torment.

Spared that trouble, at least, Stanley and the Professor and I walked down to the fortification we had so hastily contrived. It was finished.

And none too soon: the vibration indicator in the palace vault told us that only two feet of rock separated us from the burrowing monsters!

The Professor's scheme had been to cut a long slot down through the rock floor of the city to the roof of the vast, mysterious body of water below.

This slot was placed directly in front of the spot in the city wall where the Quabos were about to emerge. As they forced through the last sh.e.l.l of rock, the deluge of water, instead of drowning the city, was supposed to drain down the oblong vent. Any Quabos that were too near the tunnel entrance would be swept down too.

In silence we approached the edge of the great trough and stared down.

There was a stratum of black granite, fortunately only about thirty feet thick at this point, and then--the depths! A low roar reached our ears from far, far beneath us. A steady blast of ice cold air fanned up against us.

The Professor threw down a large fragment of rock. Seconds elapsed and we heard no splash. The unseen surface was too far below for the noise of the rock's fall to carry on up to us.

"The mystery of this ball of earth on which we live!" murmured the Professor. "Here is this enormous underground body of water. We are far below sea level. Where, then, is it flowing? What does it empty into?

Can it be that our planet is honeycombed with such hollows as this we are in? And is each inhabited by some form of life?"

He sighed and shook his head.

"The thought is too big! For, if that were true, wouldn't the seas be drained from the surface of the earth should an accidental pa.s.sage be formed from the ocean bed down to such a giant river as this beneath us?

How little we know!"

The wild clamor of an alarm bell interrupted his musing. From all the city houses poured ma.s.ses of people, to form in solid lines behind the large well.

In addition to men, there were many women in those lines, tall and strong, ready to stand by their mates as long as life was left them.

There were children, too, scarcely in their teens, prepared to fight for the existence of the race. Every able-bodied Zyobite was mustered against the cold-blooded Things that pressed so near.

The arms of these desperate fighters were pitiful compared to our own war weapons. With no need in the city for fighting engines, none had ever been developed. Now the best that could be had was a sort of ax, used for dissecting the mound-fish, and various knives fashioned for peaceful purposes.

Again the bell clamored forth a warning, this time twice repeated. Every hand grasped its weapon. Every eye went hopefully to the hole in the floor on which our immediate fate depended, then valiantly to the section of wall above it.

This quivered perceptibly. A heavy, pointed instrument broke through; was withdrawn; and a hissing stream of water spurted out.

The Quabos were about to break in upon us!

With a crash that made the solid rock tremble, a section of the wall collapsed. It was the top half of the end of the Quabos' tunnel. They had so wrought that the lower half stayed in place--a thing we did not have time to recognize as significant until later.

A solid wall of water, in which writhed dozens of tentacled monsters, was upon us, and we had time for nothing but action.

The ditch had of necessity been placed directly under the Quabos'

entrance. The first rush of water carried half over it. With it were borne scores of the cold-blooded invaders.

In an instant we were standing knee deep in a torrent that tore at our footing, while we hacked frantically with knives and axes at the slimy tentacles that reached up to drag us under.

A soft, horrible ma.s.s swept against my legs. I was overthrown. A tentacle slithered around my neck and constricted viciously like a length of rotten cable. I sawed at it with the long, notched blade I carried. Choking for air, I felt the pressure relax and scrambled to my knees.

Two more tentacles went around me, one winding about my legs and the other crushing my waist. Two huge eyes glared fiendishly at me.

I plunged the knife again and again into the barrel-shaped head. It did not bleed: a few drops of thin, yellowish liquid oozed from the wounds but aside from this my slashing seemed to make no impression.

In a frenzy I defended myself against the nightmare head that was winding surely toward me. Meanwhile I devoted every energy to keeping on my feet. If I ever went under again--

It seemed to me that the creature was weakening. With redoubled fury I hacked at the spidery shape. And gradually, when it seemed as though I could not withstand its weight and crushing tentacles another second, it slipped away and floated off on the shallow, roaring rapids.

For a moment I stood there, catching my breath and regaining my strength. Shifting, terrible scenes flashed before my eyes.

A tall Zyobite and an almost equally stalwart woman were both caught by one gigantic Quabo which had a tentacle around the throat of each. The man and woman were chopping at the viscous, gruesome head. One of the Thing's eyes was gashed across, giving it a fearsome, blind appearance.

It heaved convulsively, and the three struggling figures toppled into the water and were swirled away.

The Professor was almost buried by a Quabo that had all four of its tentacles wound about him. As methodically as though he were in a laboratory dissecting room, he was cutting the slippery lengths away, one by one, till the fourth parted and left him free.

A giant Zyobite was struggling with two of the monsters. He had an ax in each hand, and was whirling them with such strength and rapidity that they formed flashing circles of light over his head. But he was torn down at last and borne off by the almost undiminished flood that gushed from the tunnel.

And now, without warning, a heavy soft body flung against my back, and the accident most to be dreaded in that melee occurred.

I was knocked off my feet! My head was pressed under the water. On my chest was a ma.s.s that was yielding but immovable, soft but terribly strong. Animated, firm jelly! I had no chance to use my knife. My arms were held powerless against my sides.

Water filled my nose and mouth. I strangled for breath, heaving at the implacable weight that pinned me helpless. Bright spots swirled before my eyes. There was a roaring in my ears. My lungs felt as though filled with molten lead. I was drowning....

Vaguely I felt the pressure loosen at last. An arm--with good, solid flesh and bone in it--slipped under my shoulders and dragged me up into the air.

"Don't you know--can't drown a fish--holding it under water?" panted a voice.

I opened my eyes and saw Stanley, his face pale with the thrill of battle, his chin jutting forward in a berserk line, his eyes snapping with eager, wary fires.