A World is Born, Leigh Brackett, Comet, July 1941. Note: The copyright for this story has expired in the United States and, thus, now resides in the public domain. 

The rustle of cloth, the furtive creak of leather, the clink of metal equipment. Heavy breathing. Somebody whispered,
"Who the hell's that back there?"
"Must be men from the Project. We'd better hurry."
"We've got to find that damned Gray first," snapped the first voice grimly. "Caron'll burn us if we don't."
Gray counted six separate footsteps, trying to allow for the echoes. When he was sure the last man was by, he stepped out. The noise of Dio's hunt was growing--there must be a good many of them.
Covered by their own echoes, he stole up on the men ahead. His groping hand brushed gently against the clothing of the last man in the group. Gauging his distance swiftly, he went into action.
One hand fastened over the fellow's mouth. The other, holding a good-sized rock, struck down behind the ear. Gray eased the body down with scarcely a sound.
Their uniforms, he had noticed, were not too different from his prison garb. In a second he had stripped goggles, cap, and gun-belt from the body, and was striding after the others.
They moved like five eerie shadows now, in the queer light of the leader's lamp. Small fluorescent markings guided them. The last man grunted over his shoulder,
"What happened to you?"
"Stumbled," whispered Gray tersely, keeping his head down. A whisper is a good disguise for the voice. The other nodded.
"Don't straggle. No fun, getting lost in here."
The leader broke in. "We'll circle again. Be careful of that Project bunch--they'll be using ordinary light. And be quiet!"
They went, through connecting passages. The noise of Dio's party grew ominously loud. Abruptly, the leader swore.
"Caron or no Caron, he's gone. And we'd better go, too."
He turned off, down a different tunnel, and Gray heaved a sigh of relief, remembering the body he'd left in the open. For a time the noise of their pursuers grew remote. And then, suddenly, there was an echoing clamor of footsteps, and the glare of torches on the wall of a cross-passage ahead.
Voices came to Gray, distorted by the rock vaults.
"I'm sure I heard them, just then." It was Jill's voice.
"Yeah." That was Dio. "The trouble is, where?"
The footsteps halted. Then, "Let's try this passage. We don't want to get too far into this maze."
Caron's leader blasphemed softly and dodged into a side tunnel. The man next to Gray stumbled and cried out with pain as he struck the wall, and a shout rose behind them.
The leader broke into a run, twisting, turning, diving into the maze of smaller tunnels. The sounds of pursuit faded, were lost in the tomblike silence of the caves. One of the men laughed.
"We sure lost 'em!"
"Yeah," said the leader. "We lost 'em, all right." Gray caught the note of panic in his voice. "We lost the markers, too."
"You mean...?"
"Yeah. Turning off like that did it. Unless we can find that marked tunnel, we're sunk!"
Gray, silent in the shadows, laughed a bitter, ironic laugh.
-- -- -- -- -- -- -- -- -- --
They went on, stumbling down endless black halls, losing all track of branching corridors, straining to catch the first glint of saving light. Once or twice they caught the echoes of Dio's party, and knew that they, too, were lost and wandering.
Then, quite suddenly, they came out into a vast gallery, running like a subway tube straight to left and right. A wind tore down it, hot as a draught from the burning gates of Hell.
It was a moment before anyone grasped the significance of that wind. Then someone shouted,
"We're saved! All we have to do is walk against it!"
They turned left, almost running in the teeth of that searing blast. And Gray began to notice a peculiar thing.
The air was charged with electricity. His clothing stiffened and crackled. His hair crawled on his head. He could see the faint discharges of sparks from his companions.
Whether it was the effect of the charged air, or the reaction from the nervous strain of the past hours, Mel Gray began to be afraid.
Weary to exhaustion, they struggled on against the burning wind. And then they blundered out into a cave, huge as a cathedral, lighted by a queer, uncertain bluish light.
Gray caught the sharp smell of ozone. His whole body was tingling with electric tension. The bluish light seemed to be in indeterminate lumps scattered over the rocky floor. The rush of the wind under that tremendous vault was terrifying.
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.
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.