It was an amoeba, another of those single-celled, protoplasmic mounds of flesh. It had evidently come down through the hole; and now it was stretching, rubber-like, lower and lower, a living, reaching stalact.i.te of whitish hunger.

Quade was all unconscious of it. His final words reached Phil's consciousness.

"... And this time, of course, I will keep the top disintegrators on.

No other monster will then be able to weigh me down!"

He shrugged his shoulders and turned to the door. And that movement was the signal that brought his doom. Without a sound, the poised ma.s.s above dropped.

James Quade never knew what hit him. The heap of whitish jelly fell squarely. There was a brief moment of frantic lashing, of tortured struggles--then only tiny ripples running through the monster as it fed.

Sue Guinness turned her head. But the two men for some reason could not take their eyes away....

It was the girl's voice that jerked them back to reality. "The other!"

she gasped. "It's coming, behind!"

They had completely forgotten the ma.s.s in the tunnel. Turning, they saw that it was only fifteen feet away and approaching fast, and instinctively they ran out into the cavern, skirting the sphere widely. When they came to Quade's wrecked borer Phil, who had s.n.a.t.c.hed a glance behind, dragged them down behind it. For he had seen their pursuer abandon the chase and go to share in the meal of its fellow.

"We'd best not get too far away," he whispered. "When they leave the front of the borer, maybe we can make a dash for it."

For minutes that went like hours the young man watched, waiting for the creatures to be done, hoping that they would go away. Fortunately the sphere lay between, and he was not forced to see too much. Only one portion of one of the monsters was visible, lapping out from behind the machine....

At last his body tensed, and he gripped Sue and her father's arm in quick warning. The things were leaving the sphere. Or, rather, only one was. For Phil saw that they had agglutenated--merged into oneness--and now the monster that remained was the sum of the sizes of the original two. And more....

They all watched. And they all saw the amoeba stop, hesitate for a moment--and come straight for the wrecked borer behind which they were hidden.

"d.a.m.n!" Phil whispered hoa.r.s.ely. "It's still hungry--and it's after us!"

David Guinness sighed wearily. "It's heavy and sluggish, now," he said, "so maybe if we run again.... Though I don't know how I can last any longer...."

Holmes did not answer. His eyes were narrowed; he was casting about desperately for a plan. He hardly felt Sue's light touch on his arm as she whispered:

"In case, Phil--in case.... This must be good-by...."

But the young man turned to her with gleaming eyes. "Good-by, nothing!" he cried. "We've still got a card to play!"

She stared at him, wondering if he had cracked from the strain of what he had pa.s.sed through. But his next words a.s.sured her he had not. "Go back, Sue," he said levelly. "Go far back. We'll win through this yet."

She hesitated, then obeyed. She crept back from the wrecked borer, back into the dim rear, eyes on Phil and the sluggish ma.s.s that moved inexorably towards him. When she had gone fifteen or twenty yards she paused, and watched the two men anxiously.

Phil was talking swiftly to Professor Guinness. His voice was low and level, and though she could not hear the words she could catch the tone of a.s.surance that ran through them. She saw her father nod his head, and he seemed to make the gesture with vigor. "I will," she heard him say; and he slapped Phil on the back, adding: "But for G.o.d's sake, be careful!"

And with these words the old man wormed inside Quade's wrecked borer and was gone from the girl's sight.

She wanted desperately to run forward and learn what Phil intended to do, but she restrained herself and obeyed his order. She waited, and watched; and saw the young man stand up, look at the slowly advancing monster--and deliberately walk right into its path!

Sue could not move from her fright. In a daze she saw Phil advance cautiously towards the amoeba and pause when within five feet of it.

The thing stopped; remained absolutely motionless. She saw him take another short step forward. This time a pseudopod emerged, and reached slowly out for him. Phil avoided it easily, but by so narrow a margin that the girl's heart stopped beating. Then she saw him step back; and, snail-like, the creature followed, pausing twice, as if wary and suspicious. Slowly Phil Holmes drew it after him.

To Sue, who did not know what was his plan, it seemed a deliberate invitation to death. She forgot about her father, lying inside the mangled borer, waiting. She did not see that Phil was leading the monster directly in front of it....

It was a grotesque, silent pursuit. The creature appeared to be unalert; its movements were sloth-like; yet the girl knew that if Phil once ventured an inch too close, or slipped, or tried to dodge past it to the sphere, its torpidness would vanish and it would have him. His maneuvering had to be delicate, judged to a matter of inches. Tense with the suspense, the strain of the slow-paced seconds, she watched--and yet hardly dared to watch, fearful of the awful thing she might see.

It was a fantastic game of tag her lover was playing, with death the penalty for tardiness. The slow, enticing movements were repeated again and again, Phil advancing very close, and stepping back in the nick of time. Always he barely avoided the clutching white arms that were extended, and little by little he decoyed the thing onward....

Then came the end. As Holmes was almost in front of the wrecked machine, Sue saw him glance quickly aside--and, as if waiting for that moment when he would be off guard, the monster whipped forward in a great, reaching surge.

Sue's ragged nerves cracked: she shrieked. They had him! She started forward, then halted abruptly. With a tremendous leap, Phil Holmes had wrenched free and flung himself backwards. She heard his yell:

"Now!"

There was a sputter from the bottom of the outstretched borer; then, like the crack of a whip, came a bellow of awful sound.

A thick cloud of dust reared up, and the ear-numbing thunder rolled through the cavern in great pulsing echoes. And then Sue Guinness understood what the young man had been about.

The disintegrators of James Quade's borer had sent a broad beam of annihilation into the monster. His own machine had destroyed his destroyer--and given his intended victims their only chance to escape from the dread fate he had schemed for them.

Sue could see no trace of the creature in its pyre of slow-swirling dust. Caught squarely, its annihilation had been utter. And then, through the thunder that still echoed in her ear-drums, she heard a joyful voice.

"We got 'em!"

Through the dusty haze Phil appeared at her side. He flung his arms up exultantly, swept her off the ground, hugged her close.

"We got 'em!" he cried again. "We're free--free to go up!"

Professor David Guinness crawled from the borer. His face, for the first time since the descent, wore a broad smile. Phil ran over to him, slapped him on the back; and the older man said:

"You did it beautifully, Phil." He turned to Sue. "He had to decoy them right in front of the disintegrators. It was--well, it was magnificent!"

"All credit to Sue: she was my inspiration!" Phil said, laughing. "But now," he added, "let's see if we can fix those dead rocket-tubes. I have a patient up above--and, anyway, I'm not over-fond of this place!"

The three had won through. They had blasted four miles down from the surface of the earth. The brain of an elderly scientist, the quick-witted courage of a young engineer, had achieved the seemingly impossible--and against obstacles that could not have been predicted.

Death had attended that achievement, as death often does accompany great forward steps; James Quade had gone to a death more hideous than that he devised for the others. But, in spite of the justice of it, a moment of silence fell on the three survivors as they came to the spot where his fate at last had caught up to him.

But it was only a moment. It was relieved by Professor Guinness's picking up the chunk of radium ore his former partner had hewn from the cavern's wall. He held it up for all to see, and smiled.

"Here it is," he said simply.

Then he led the way into his earth-borer, and the little door closed quietly and firmly into place.