They stopped, Gray keeping to the background. Now was the time to evade his unconscious helpers. The moment they reached daylight, he'd be discovered. Soft-footed as a cat, he was already hidden among the heavy shadows of the fluted walls when, he heard the voices. They came from off to the right, a confused shout of men under fearful strain, growing louder and louder, underscored with the tramp of footsteps. Lights blazed suddenly in the cathedral dark, and from the mouth of a great tunnel some hundred yards away, the men of the Project poured into the cave. And then, sharp and high and unexpected, a man screamed. * * * * * The lumps of blue light were moving. And a man had died. He lay on the rock, his flesh blackened jelly, with a rope of glowing light running from the metal of his gun butt to the metal buttons on his cap. All across the vast floor of that cavern the slow, eerie ripple of motion grew. The scattered lumps melted and flowed together, converging in wavelets of blue flame upon the men. The answer came to Gray. Those things were some form of energy-life, born of the tremendous electric tensions on Mercury. Like all electricity, they were attracted to metal. In a sudden frenzy of motion, he ripped off his metal-framed goggles, his cap and gun-belt. The Moultons forbade metal because of the danger of lightning, and his boots were made of rubber, so he felt reasonably safe, but a tense fear ran in prickling waves across his skin. Guns began to bark, their feeble thunder all but drowned in the vast rush of the wind. Bullets struck the oncoming waves of light with no more effect than the eruption of a shower of sparks. Gray's attention, somehow, was riveted on Jill, standing with Dio at the head of her men. She wore ordinary light slippers, having been dressed only for indoors. And there were silver ornaments at waist and throat. He might have escaped, then, quite unnoticed. Instead, for a reason even he couldn't understand, he ran for Jill Moulton. The first ripples of blue fire touched the ranks of Dio's men. Bolts of it leaped upward to fasten upon gun-butts and the buckles of the cartridge belts. Men screamed, fell, and died. An arm of the fire licked out, driving in behind Dio and the girl. The guns of Caron's four remaining men were silent, now. Gray leaped over that hissing electric surf, running toward Jill. A hungry worm of light reared up, searching for Dio's gun. Gray's hand swept it down, to be instantly buried in a mass of glowing ropes. Dio's hatchet face snarled at him in startled anger. Jill cried out as Gray tore the silver ornaments from her dress. "Throw down the guns!" he yelled. "It's metal they want!" He heard his name shouted by men torn momentarily from their own terror. Dio cried, "Shoot him!" A few bullets whined past, but their immediate fear spoiled both aim and attention.