But with his body taut, his leg muscles almost vibrating in the first part-instant of contraction, there was a sudden hoarse cry of utter surprise in Bigman's ears.

They were standing there, both of them, in a gray, dark world in which their beams of light etched one another out. Outside the beams of light, nothing, so that the sudden blob of motion that flashed across the line of sight made no sense at first.

His first reaction, his first thought was: Lucky! Had Lucky returned? Had he somehow mastered the situation, turned the tables?

But there was motion again, and the thought of Lucky faded away.

It was as though a fragment of the rocky wall of the shaft had worked itself loose and was drifting downward in the lazy fall that was characteristic of Mercury's low gravity.

A rope of rock that was somehow flexible, that struck Urteil's shoulder and-clung. One such encircled his waist already. Another moved slowly, bringing itself down and around as though it were part of an unreal world of slowed motion. But as its edge circled Urteil's arm and touched the metal covering Urteil's chest, arm and chest closed upon one another. It was as though the sluggish and seemingly brittle rock contained the irresistible strength of a boa constrictor.

If Urteil's first reaction had been one of surprise, there was now nothing but complete terror in his voice.

"Cold," he croaked harshly. "They're cold."

Bigman's whirling mind was having trouble encompassing the new situation. A piece of that rock had encircled Urteil's lower arm and wrist. The butt of the blaster was clamped in place.

A final rope came floating down. They were so rock-like in appearance that they were invisible until one actually detached itself from the wall.

The ropes were connected one with another as a single organism, but there was no nucleus, no "body." It was like a stony octopus consisting of nothing but tentacles.

Bigman had a kind of explosion of thought.

He thought of rock developing life through the long ages of Mercurian evolution. A completely different form of life from anything Earth knew. A life that lived on scraps of heat alone.

Why not? The tentacles might crawl from place to place, seeking any bit of heat that might exist. Bigman could see them drifting toward Mercury's North Pole when mankind was first established there. First the mines and then the Observatory Dome supplied them with unending trickles of heat.

Man could be their prey too. Why not? A human being was a source of heat. Occasionally an isolated miner might have been trapped. Paralyzed with sudden cold and terror, he would be unable to call for help. Minutes later his power unit would be too low to make a radio call possible in any case. Still later, he would be dead, a frozen relic.

Cook's mad story of the deaths in the mines made sense.

All this passed through Bigman's mind almost in one flash while he remained unmoving, still struggling with a sense of stunned amazement at the sudden new turn of events.

Urteil's voice was somewhere between a moan and a harsh gasp. "I-can't… Help me-help-^: - It's cold-cold… "

Bigman yelled, "Hold on. I'm coming."

Gone in a moment was any thought that this man was an enemy, that moments before he had been on the point of killing Bigman in cold blood. The little Martian recognized but one thing; here was a man, helpless in the grip of something nonhuman.

Since man had first left Earth and ventured into the dangers and mysteries of outer space, there had grown up a stern, unwritten law. Human feuds must be forgotten when man faced the common enemy, the non-human and inhuman forces of the other worlds.

It might be that not everyone adhered to that law, but Bigman did.

He was at Urteil's side in a bound, tearing at his arm.

Urteil mumbled, "Help me… "

Bigman grasped at the blaster Urteil still held, trying to avoid the tentacle that encircled Urteil's clutching fist. Bigman noted absently that the tentacle didn't curve smoothly like a snake would. It bent in sections as though arranged in numerous stiff segments hinged together.

Bigman's other hand, groping for purchase on Ur-teil's suit, made momentary contact with one of the tentacles and sprang away reflectively. The cold was an icy shaft, penetrating and burning his hand.

Whatever method the creatures had of withdrawing heat, it was like nothing he had ever heard of.

Bigman yanked desperately at the blaster, heaving and wrenching. He did not notice at first the alien touch on his back, then-iciness lay over him and did not go away. When he tried to jump away he found he could not. A tentacle had reached out for him and embraced him.

The two men might have grown together, so firmly were they bound.

The physical pain of the cold grew, and Bigman wrenched at the blaster like a man possessed. Was it giving?

Urteil's voice startled him as it murmured, "No use… "

Urteil staggered and then, slowly, under the weak pull of Mercury's gravity, he toppled over to one side, carrying Bigman with him.

Bigman's body was numb. It was losing sensation. He could scarcely tell whether he was still holding the muzzle of the blaster or not. If he was, was it yielding to his wild, sidewise wrenches, or was it a last gasp of wishful thinking?

His suit-light was dimming as his power-unit drained much of its energy into the voracious power-sucking ropes.

Death by freezing could not be far away.

Lucky, having left Bigman in the mines of Mercury, and having changed to an inso-suit in the quiet of the hangared Shooting Starr, stepped out onto the surface of Mercury and turned his face toward the "white ghost of the Sun."

For long minutes he stood motionless, taking in once again the milky luminescence of the Sun's corona.

Absently, as he watched, he flexed his smoothly-muscled limbs one at a time. The inso-suit worked more smoothly than an ordinary space-suit. That, combined with its lightness, lent it an unusual sensation of not being there altogether. In an environment obviously airless, it was disconcerting, but Lucky brushed aside any feeling of uneasiness he might have had and surveyed the sky.

The stars were as numerous and brilliant as in open space, and he paid them little attention. It was something else he wanted to see. It was two days now, standard Earth time, since he had last seen these skies. In two days, Mercury had moved one forty-fourth of the way along its orbit around the Sun. That meant over eight degrees of sky had appeared in the east and over eight degrees had disappeared in the west. That meant news stars could be seen.

New planets too. Venus and Earth ought both to have risen above the horizon in the interval.

And there they were. Venus was the higher of the two, a diamond-bright bit of white light, much more brilliant than it ever appeared to be on Earth. From Earth, Venus was seen at a disadvantage. It was between Earth and the Sun, so that when Venus was closest, Earth could see only its dark side. On Mercury, Venus could be seen at the full.

At the moment, Venus was thirty-three million miles from Mercury. At the closest, however, it could approach to within almost twenty million miles, and then keen eyes could actually see it as a tiny disk.

Even as it was, its light almost rivaled that of the corona, and, staring at the ground, Lucky thought he could make out a double shadow extending from his feet, one cast by the corona (a fuzzy one) and one by Venus (a sharp one). He wondered if, under ideal circumstances, there might not be a triple shadow, the third being cast by Earth itself.

He found Earth, too, without difficulty. It was quite near the horizon, and, though it was brighter than any star or planet in its own skies, it was pale in comparison to the glorious Venus. It was less brightly lit by its more distant Sun; it was less cloudy and therefore reflected less of the light it did give. Furthermore, it was twice as far from Mercury as Venus was.

Yet in one respect it was incomparably more interesting. Where Venus's light was a pure white, Earth's light was a blue-green glow.

And more than that, there was near it, just skirting the horizon, the smaller yellow light of Earth's Moon. Together, Earth and Moon made a unique sight in the skies of the other planets inside the orbit of Jupiter. A double planet, traveling majestically across the skies in each other's company, the smaller circling the larger in a motion which, against the sky, looked like a slow wobble from side to side.

Lucky stared at the sight perhaps longer than he should have, yet he could not help it. The conditions of his life took him far from his home planet on occasion, and that made it all the dearer to him. All the quadrillions of human beings throughout the Galaxy had originated on Earth. Through almost all of man's history, Earth had been his only home, in fact. What man could look on Earth's speck of light without emotion?

Lucky tore his eyes away, shaking his head. There was work to be done.

He set out with firm stride toward the coronal glow, skimming close to the surface as was proper in low gravity, keeping his suit-light on and his gaze fixed at the ground before him in order to guard against its rough unevenness.

He had an idea of what he might find, but it was purely a notion, backed as yet by no definite fact. Lucky had a horror of discussing such notions, which were sometimes nothing more than intuitions. He even disliked lingering on them in his own mind. There was too great a danger of growing used to the idea, of beginning to depend upon it as truth, of closing the mind unintentionally to alternate possibilities.

He had seen this happen to the ebullient, ready-to-believe, ready-to-act Bigman. He had watched vague possibilities become firm convictions in Bigman's mind more than once…

He smiled gently at the thought of the little bantam. Injudicious he might be, levelheaded never, but he was loyal and ablaze with fearlessness. Lucky would rather have Bigman at his side than a fleet of armored space-cruisers manned by giants.

He missed the gnome-faced Martian now, as he leaped flatly along the Mercurian terrain, and it was partly to wipe out that uncomfortable sensation that Lucky returned to thoughts of the problem at hand.

The trouble was that there were so many crosscurrents.

First, there was Mindes himself, nervous, unstable, unsure of himself. It had never been entirely settled, really, how far his attack on Lucky had been momentary madness and how far settled calculation. There was Gardoma, who was Mindes's friend. Was he a dedicated idealist caught up in the dream of Project Light, or was he with Mindes for purely practical reasons? If so, what were they?