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.
Gray caught up Jill and began to run, toward the tube from which the wind howled in the cave. Behind him, grimly, Dio followed.
The electric beasts didn’t notice him. His insulated feet trampled through them, buried to the ankle in living flame, feeling queer tenuous bodies break and reform.
The wind met them like a physical barrier at the tunnel mouth. Gray put Jill down. The wind strangled him. He tore off his coat and wrapped it over the girl’s head, using his shirt over his own. Jill, her black curls whipped straight, tried to fight back past him, and he saw Dio coming, bent double against the wind.
He saw something else. Something that made him grab Jill and point, his flesh crawling with swift, cold dread.
*
The electric beasts had finished their pleasure. The dead were cinders on the rock. The living had run back into the tunnels. And now the blue sea of fire was flowing again, straight toward the place where they stood.
It was flowing fast, and Gray sensed an urgency, an impersonal haste, as though a command had been laid upon those living ropes of flame.
The first dim rumble of thunder rolled down the wind. Gripping Jill, Gray turned up the tunnel.
The wind, compressed in that narrow throat of rock, beat them blind and breathless, beat them to their bellies, to crawl. How long it took them, they never knew.
But Gray caught glimpses of Dio the Martian crawling behind them, and behind him again, the relentless flow of the fire-things.
They floundered out onto a rocky slope, fell away beneath the suck of the wind, and lay still, gasping. It was hot. Thunder crashed abruptly, and lightning flared between the cliffs.
Gray felt a contracting of the heart. There were no cables.
Then he saw it--the small, fast fighter flying below them on a flat plateau. A cave mouth beside it had been closed with a plastic door. The ship was the one that had followed them. He guessed at another one behind the protecting door.
Raking the tumbled blond hair out of his eyes, Gray got up.
Jill was still sitting, her black curls bowed between her hands. There wasn’t much time, but Gray yielded to impulse. Pulling her head back by the silken hair, he kissed her.
“If you ever get tired of virtue, sweetheart, look me up.” But somehow he wasn’t grinning, and he ran down the slope.
He was almost to the open lock of the ship when things began to happen. Dio staggered out of the wind-tunnel and sagged down beside Jill. Then, abruptly, the big door opened.
Five men came out--one in pilot’s costume, two in nondescript apparel, one in expensive business clothes, and the fifth in dark prison garb.
Gray recognized the last two. Caron of Mars and the errant Ward.
They were evidently on the verge of leaving. But they looked cheerful. Caron’s sickly-sweet face all but oozed honey, and Ward was grinning his rat’s grin.
Thunder banged and rolled among the rocks. Lightning flared in the cloudy murk. Gray saw the hull of a second ship beyond the door. Then the newcomers had seen him, and the two on the slope.
Guns ripped out of holsters. Gray’s heart began to pound slowly. He, and Jill and Dio, were caught on that naked slope, with the flood of electric death at their backs.
His Indianesque face hardened. Bullets whined round him as he turned back up the slope, but he ran doubled over, putting all his hope in the tricky, uncertain light.
Jill and the Martian crouched stiffly, not knowing where to turn. A flare of lightning showed Gray the first of the firethings, flowing out onto the ledge, hidden from the men below.
“Back into the cave!” he yelled. His urgent hand fairly lifted Dio. The Martian glared at him, then obeyed. Bullets snarled against the rock. The light was too bad for accurate shooting, but luck couldn’t stay with them forever.
Gray glanced over his shoulder as they scrambled up on the ledge. Caron waited by his ship. Ward and the others were charging the slope. Gray’s teeth gleamed in a cruel grin.
Sweeping Jill into his arms, he stepped into the lapping flow of fire. Dio swore viciously, but he followed. They started toward the cave mouth, staggering in the rush of the wind.
“For God’s sake, don’t fall,” snapped Gray. “Here they come!”
The pilot and one of the nondescript men were the first over. They were into the river of fire before they knew, it, and then it was too late. One collapsed and was buried. The pilot fell backward, and then other man died under his body, of a broken neck.
Ward stopped. Gray could see his face, dark and hard and calculating. He studied Gray and Dio, and the dead men. He turned and looked back at Caron. Then, deliberately, he stripped off his gun belt, threw down his gun, and waded into the river.
Gray remembered, then, that Ward too wore rubber boots, and had no metal on him.
*
Ward came on, the glowing ropes sliding surf-like around his boots. Very carefully. Gray handed Jill to Dio.
“If I die too,” he said, “there’s only Caron down there. He’s too fat to