"But isn't there any way around it? Look, over there to the left. One edge of the crater seems to end almost underneath us."

It was true that the center of the caldron was far to the right of where they stood, and that its left rim was only a little within their direct line of descent. But to land even one foot inside that inferno would be as fatal as to alight in its very midst.

Kendrick was thinking fast.

"There's just a chance," he said. "It all depends upon how wide the zone of these escalator rays is, and whether we can tune in on them.

At least, I can probably answer the latter question."

Pushing the protrudent round b.u.t.ton on his mysterious bracelet as he spoke, he leaned over the edge of the trap-door and awaited results.

They were not long in coming. The vibration he was already under from the invisibility rays seemed to double. Alternate waves of giddiness and depression, of push and pull, swept over him.

A minute of it was enough. He pressed the round b.u.t.ton that now protruded, ending this influence, and faced Marjorie, stating:

"I'm positive now that these things control descent and ascent. As nearly as I can figure, the rays work on the principle of an endless belt. If you're up here, you get carried down, and vice versa. As to how wide the belt is, and whether you can move sideways on it, remains to be seen. Anyway, I'm going to take a chance. I'll go first. If my guess is wrong, you--well, needn't follow."

"No, I'm going with you!" she declared resolutely. "We've come this far together. I shan't be left alone now. Let's go!"

And again her soft, warm hand was in his.

Lord, what a girl! How many would be brave enough to take a gamble like that, on a fellow's mere supposition?

"All right--go it is!" he said. "Push your round b.u.t.ton, like this."

He showed her the way he thought was right, pushed his own. "Ready?"

"Ready!"

Their voices were grave. It was a grim prospect, stepping off into s.p.a.ce like that, with only a guess between them and death.

"Then jump!"

They jumped, gripping each other's hands tightly--and instead of dropping like plummets were caught in a powerful field of force and whirled gently downward.

"Oh, you were right!" gasped Marjorie, awed. "See, we--"

Then she paused, horror-stricken, for it was obvious that they were to descend within that lake of molten gla.s.s, unless they could change their course at once.

"Quick!" he called. "Hold fast! Now--run!"

Breathless, they raced to the left, across that invisible descending belt.

Too far, Kendrick knew, and they would plunge outside its zone, fall crushed and mangled. Not far enough, and they would meet cremation. It was a fearful hazard, either way, but it had to be taken.

They were almost down, now, and still not quite far enough to the left. The heat of that yawning crater rose toward them.

"Faster--_faster_!" he cried, fairly dragging her along with him.

A last dash--a breathless instant--and they stood there on the ground, not three feet from the edge of doom.

Swooning with the heat, Marjorie swayed against him, murmured an incoherent prayer.

"Take heart!" he whispered, lifting her bodily and bearing her some yards away. "We're down--safe!"

Their safety was but relative, however, Kendrick well knew. Until they could put miles between them and this monstrous disc, they were not really safe. No telling how soon their escape might be discovered. No telling what terrible means Cor might take of curbing their flight.

So as soon as Marjorie had recovered sufficiently to proceed, they headed off across the desert at a fast walk toward Ajo, where he hoped to catch the afternoon train for Gila Bend. From there, they could board the limited for Tucson and points east, when it came through from Yuma that night.

They had tuned out on the escalator rays, but continued on still invisible--for the disc hung above them in plain view and it would have been suicide to let themselves be seen.

Even so, Kendrick soon began to have an uneasy feeling of being followed. He looked around from time to time, but could see nothing.

Were some of those invisible little creatures on their trail?

He said nothing to Marjorie of his anxiety, but presently she too began glancing backward uneasily, every few steps.

"They are near us!" she said at length, in a whisper. "I can sense them."

It was more than sense, they soon discovered. Little paddings became quite audible, and once or twice they saw the sand scuffed up, not twenty feet away, as though by a foot pa.s.sing over it.

Meanwhile they were climbing a rise of ground, broken by many small hummocks and dotted with th.o.r.n.y shrubs. On the other side, at the foot of a long down-slope, lay Ajo.

Once they reached the summit, Kendrick felt sure they could outdistance their pursuers on the descent. Already, if his watch was right, the train was preparing to pull out. It would be a breathless dash, but he was confident they could make it.

So he rea.s.sured Marjorie as best he could, and helped her on up the slope.

They were practically on the summit and already in view of the little railroad station and huddle of shacks below--when suddenly he felt himself tripped and flung violently to the ground. At the same instant, his companion emitted a scream, as she felt herself seized by invisible hands.

Leaping to his feet, Kendrick flailed out with solid fists at their attackers. Groans answered the impacts and he knew his blows were taking effect.

Free for a moment he dashed to Marjorie, felt for the midgets who swarmed around her. Seizing one of the invisible forms, he lifted it and flung it crashing to the ground. Another, likewise, and another.

Then he threshed his legs, where two of the creatures clung, trying to drag him down again. They flew through the air, with cries of fright.

"Well, so far, so good!" he exclaimed. "We won't wait to see if there are any more. Come on--let's go!"

"Right!"

Reaching for each other's hands, they raced down the slope.