But his further reflections were not so satisfying. "Who did it? How? Where did they go?" He was echoing Smithy's questions and finding no ready answers. And that flame-thrower that had cut down old Riley--how was that worked? Its one green flash had been almost instantaneous. He was puzzling over such futile questioning when he saw the first sign of attack. * * * * * At the foot of the derrick was the hoisting shed. Except for that, there was clear sand for a radius of fifty feet around the derrick's base. Dean was staring suspiciously at that open space almost directly underneath. Moving sand! He hardly knew what he had seen at first. Then the sand at one point bulged upward unmistakably. For one instant Dean's thoughts shot off at a tangent. It was like the work of a huge gopher--he had seen the little animals break through like that. Then the sand parted, and something, indistinct, blurred, dark against the yellow background, broke from cover. Rawson swung the rifle's muzzle over and down. Below him the vague shadow had moved. Dean caught the blurred mass beyond his sights, then swung the weapon aside. Who was it? He would have a look first. The thin crack of his rifle ripped the silence of the sleeping camp. Dean had aimed to one side and he regretted it in the instant of firing. For, in the same second, there had come from the moving shadow the gleam of starlight reflected upward from polished metal. * * * * * Dean swung the rifle back. He fired quickly a second time. Beside him the big light hissed into action and the whole camp sprang to sudden, blazing light. And through the quick brilliance, more dazzling even than the white glare itself, was one blinding line of green flame. Dean saw it as it began. It came from the dim shadow that had sprung suddenly into sharp outline as the big lights came on. He saw the figure. He sensed that it was a man, though he knew vaguely that the figure was grotesque and hideous in some manner he had no time to discern. The thin line of green flame ripped straight out, swinging in a quick, sweeping trajectory, slashing through the steelwork of the great derrick itself! Dean knew he was lost in the blinding instant while that fiery jet was sweeping in a fan-shaped sector of vivid green. A knife of flame! It had destroyed a man: it was now cutting down a framework of steel as well! The derrick was falling as he fired again. There came a crushing jar downward as the metal melted and failed, and the wild outward swing in the beginning of the toppling fall. In the mind of Dean Rawson was but one thought: the sights--and a something blurred beyond--a trigger to be pressed. He was still firing when the shriek of torn steel went to thundering silence, and even the lights of Tonah Basin Camp were swallowed up in the whirling night.... CHAPTER VI _Into the Crater_