What could it have been? he demanded. He found and rejected a dozen answers before he saw, far down in the black crater-mouth, a flash of red; then heard again that ghost of a sound and knew it for what it was. Thick walls, these of the space ship, and insulated well; and the thin atmosphere of this wild world could cut a blast of sound to a mere fraction of its volume! But the walls were admitting a fragmental echo of what must have been a reverberating voice. They were quivering to the roar of exploding detonite! It was Chet! He was fighting, he was in trouble! Spud's trembling hands steadied upon the metal control; he lifted the ship as smoothly as even Chet might have done, and he drove it out and down into a throat too narrow for safety, but where the tiny, red flash of a weapon had called with an S O S as plain as any lettered call--a message to which brave men have everywhere responded. * * * * * He saw Chet but once. The master pilot had shown him the flare release lever; he moved it now, and the place of darkness was suddenly blinding with light. There were rocks close at hand; the crater had narrowed to a funnel throat that was cut and terraced as if by human hands. Below, it ended in a smooth stone floor where the lava had sealed it shut. From a terrace came the gleaming reflection of Chet's suit. Miraculously the gleam was doubled, as if another in similar garb stood at his side. And beyond, from blocks of stone, came leaping things--living creatures! The light died. Spud realized he had not opened the release lever full. He fumbled for it--found it, jammed it over! And in the light that followed he saw only empty, terraced walls where nothing moved, and a lava floor below that, for an instant, gaped open, then again was smooth and firm. And the thunder of his ship's exhausts came back to him from those threatening walls to tell of a loneliness more certain and terrible than any solitude he had found in the silence where he had waited above. But through all his dismay ran an undercurrent of puzzled wonderment. For here on a dead world, where all men agreed there could be no life, he had seen the impossible. Only one glimpse before the light had died; only for an instant had he seen the things that leaped upon Chet--but he knew! Never again could any man tell Spud O'Malley that the Moon was a lifeless globe ... and he knew that the life was of a form monstrous and horrible and malign! CHAPTER V _"And I've Brought You to This!"_ The master pilot, when he stepped forth upon that weird globe which was the Moon, found himself plunged into a spectral world. Even from within the air-tight suit, through whose helmet-glass he peered, he sensed, as he had not when inside the ship, the vast desolation, the frozen emptiness of this rocky waste.