Nellon, had failed, had narrowly escaped losing his own life because of his blunder. Intent upon the shove which was to have sent Tim Austin hurtling to his death, he had forgotten the snow-concealed ice in the trail, as lethal with hidden treachery as a patch of quick-sand.

But he was still alive. They hadn't, as yet, even reached Ryska's hut, and Nellon knew another chance would present itself. He considered this with a curious mixture of impatience and reluctance.

"If it wasn't for Big Tim—" Nellon was hearing Laura say the words again, and once again the realms of unutterable bliss he read into them strengthened his resolve. One more chance—and this time he would not fail or waver.

"Brad—look!"

Vibrant with surprise and urgency, the words ripped aside the veil of Nellon's thoughts. His head jerked up.

Big Tim was on his feet. He was pointing up at the steep bank of the gorge down which they had tumbled.

Most of the disturbed snow had settled and the wind had carried away the rest. Nellon could see quite clearly.

There up on the bank, a small snow slide had taken place. And now, against the unbroken monotony of white, something gleamed in vivid contrast.

Nellon squinted. Gradually he began to make out details. The strange surface revealed by the slide seemed to have the mellow hue of bronze, but Nellon could not be sure, since it was queerly dappled and flecked with tones of gold and red. He thought it must be from the strain on his eyes, and closed them momentarily. But when he looked again the colors were as weird as he had last seen them. This time, however, he made out a detail which he had missed previously. The surface seemed to be crossed by a black line or stripe.

"Now what in the world can that be?" Tim Austin's voice was wondering, vaguely troubled. "It's like no sample of rock or soil we've taken. Metal—that's what it is!" he exclaimed of a sudden. "It's an exposed vein of some metal. Come on, Brad, let's have a look at it."

Nellon got to his feet, his eyes fixed upon that uncanny patch of something which stood out against the surrounding whiteness like a smear of blood.

Big Tim was already started up the bank. Nellon sucked in a breath and followed after him.

The climb was a hard and difficult one, and their recent physical jarring caused by the fall made it all the harder. But curiosity pulled them on like a vast magnet. In the exertion they forgot their aches and bruises. Slipping and sliding, clutching for handholds, floundering in loose drifts which filled pockets of hardened crust, they made their way slowly but surely up the bank.

Finally they stood before that strangely mottled patch of red and brown and gold. The mood of awed wonder which gripped them at once heightened and deepened.

"It is metal!" Tim Austin breathed. "But—but, Brad, it's not a vein. It's—"

"It's a door!" Nellon finished hoarsely.

It was a door, a metal door in the snow covered bank of a falls that had, in some long, long ago, solidified to ice. A door to what? Where did it lead? What would be on the other side of it? What could be on the other side of a metal door on a world where it was doubtful that living beings had ever existed at all?

There was a rasp in Nellon's earphones. And then Big Tim Austin's voice followed it.

"Brad—I'm going in. This—why, this is the biggest find of the whole expedition!"

"It might be dangerous," Nellon pointed out, before he could become aware of the wealth of irony which lay behind the words. "We don't know what sort of life—"

"But this door has been hidden under snow for the Lord only knows how many years, Brad. Look where the crust had split here. It's thick, thick. Nothing has gone in or out for a hell of a long time. If there were beings, they're either gone or dead."

And, as if having satisfied himself on this last account, Big Tim stepped directly up to the door. He was a tall man, yet he seemed dwarfed beside it. And it was obviously very massive, for it was partly open and the width of the edge revealed could not have been spanned by the long, flexible metal fingers of their protecting gloves. The opening was a mere crack, as if someone had once made it so for a cautious glimpse of the world outside and never closed it again.

Big Tim placed his gloves against the projecting edge.

"Give me a hand, Brad. We'll see if we can open it further."

Together, they shoved. They drew upon ebbing reserves of strength, but what energy they managed to summon they threw into a brief, terrific effort to move the portal. But it did not move. Their combined strength seemed pitifully small against the weight they sought to budge.

They were about to relax their efforts in despair when, suddenly, transmitted from the metal of the door to that of their gloved hands, they felt what seemed to be a coughing whir. The sound smoothed out, deepened, and became a steady hum.

Startled, they leaped away. Their faces took on an intent, incredulous expression.

The door was opening. Slowly, majestically, it was swinging wide.

No force that they could see was behind it. The door seemed to move of its own volition. They stood as still as a pair of weird, metal statues, watching. Every sense, keyed to its highest, was directed at the widening gap.

At last all movement ceased, and the door hung wide. The humming note which had accompanied its opening dwindled to a whisper and died away. Revealed was a tunnel of utter blackness.

Tim Austin released his breath. The sound roused Nellon from the trance which gripped him.

"It's probably controlled by an automatic mechanism. When we shoved against it, we must have set that mechanism in motion."

"I'm going in, Brad," Big Tim said suddenly. "I'm going to see what's inside." He strode impulsively to the door. But at the threshold he stopped and turned and looked at Nellon.

Nellon smiled faintly and nodded. He strode after Big Tim. Together they entered the doorway.

Lights, built into the helmets of their suits, but up to this time unused, were turned on to illuminate the way. The tunnel, they saw, was a rectangular corridor or passageway. It was lined with the same metal as that of the door.

At two intervals down the corridor they found it necessary to squeeze through half-opened doorways. The doors here were of the slide type and seemed to be controlled by machinery as was the one which they had opened to gain entrance to the corridor. But these could not be moved, nor did their efforts awaken any hum of machinery.

"You know," Big Tim remarked, "this arrangement of doors sort of reminds me of an airlock."

"I've noticed the same thing," Nellon responded. "But an airlock—" He shook his head, for this was one of the many things he couldn't understand.

Soon the corridor came to an end. Nellon and Austin found themselves in a small, square room, each side of which was lined with small glass cubicles or cabinets. In each reposed a transparent sphere with various inexplicable attachments and a compactly folded mass of some strange material.

"Helmets!" Big Tim breathed. "Brad, those are helmets. And unless I'm mistaken the other stuff must be suits of some kind. What have we stumbled onto, anyway?"

Nellon passed a slow, almost-knowing glance about the room, his helmet lights glinting on the glass of the cabinets.

"I've got a crazy idea," he said. "But let that wait until we see more. There's another doorway over there. Let's go on."

They went on. There were more corridors, but this time there were rooms opening from them. Each was uniformly alike, filled with the same articles and furnishings. Nothing with which they were familiar had any counterpart here. Everything, from strange, rounded furniture to bizarre clothing, was weirdly alien.

But of the beings who had once inhabited these rooms they found no trace. There were only the