The tube twisted and turned like a snake. It sank in sharp downward angles and he lay on his back and slid like a man on a sled. He followed it without thinking where it would lead him.

Where the tunnel walls pinched together he wormed his way through. Where crevices opened in the floor, he found the strength to get across. Where the roof lowered he went on hands and knees, He kept moving.

Time lost significance. He lost all comprehension of the passing hours. His suit's chronometer, shattered in the fall into the arroyo, presented only a fixed present-time frozen, as if his life had stopped at that moment. Past, present, and future merged into one mingling amorphous element through which he moved as through water. once he came to himself as he felt the floor drop away beneath him, his feet kicking out from under him. He landed heavily on his back and glimpsed the shaft falling away in a near-vertical drop.

He had stepped over the brink without knowing it.

The tube was smooth beneath him, and the light-emitting algae cushioned his slide somewhat as he picked up momentum, sliding faster and faster, riding the curving conduit deeper into the Red Planet's heart.

The exhilaration of this wild ride burned the clouds from his mind. He felt adrenaline pumping into his bloodstream, rousing him from his torpor as the shaft raced by him, blurring his vision.

It seemed to him that he was falling into a gleaming green infinity, hurtling faster and faster, whizzing into a radiant unknown.

The luminous algae tore away in flashing streamers from his hands and feet to splatter over him like foaming light, covering his faceplate, blinding him. He wiped at the visor and cleared a small area just in time to see the shaft bottom out.

He braced himself for the impact and felt the tube curve and level out as he hit the bottom with a bone-cracking thump. He skidded out, arms and legs flailing, rolling over himself as if he'd been tossed from a speeding vehicle.

When at last he raised his head to look around he saw that he was in an enormous cavern. He pushed himself up on elbows and knees and winced from shooting pains in his head and back.

The cave was a vast bubble-shaped dome flattened on the bottom. Its roof arched at least a hundred meters above the floor; the walls, curved and smooth, lifted upward gracefully.

He rose stiffly and, feeling as if every bone in his body had been rearranged, began walking the length of the domed vault. The dim bluish-green light bathed him in the illusion of walking on the bottom of the sea; he fully expected schools of fish to swim by at any moment.

He reached the further wall and discovered that the cave had several smaller conduits leading out of it, and large drainlike holes in the floor. These smaller tubes were squat, roughly half his height; if he were to continue his journey it would have to be on hands and knees.

He quaked at the thought. His muscles already drooped with exhaustion and strain. He sank to the floor and lay down in front of one of the drain tubes. In moments he was sound asleep.

… TWO DOORS STOOD AT the end of a long, dark passage, I shimmering with a cool blue light. Spence approached the doors and as he came nearer his heart began to race, pounding his chest. Sweat rolled off his forehead and burned in his eyes.

He wiped his face with his sleeve and walked on.

Now he stood before the two doors and it came to him that behind one of the doors Ari waited to embrace him, to soothe his troubled spirit and heal his wasted body.

Behind the other door a monster with large yellow eyes hulked ready to pounce and devour him.

He wept with anguish over the decision he must make, and cried out for someone to help him, but his voice rang hollow in his ears.

He stepped forward, placed his hand on the old-fashioned doorknob, and turned. The door creaked open on ancient hinges and he peered apprehensively into the room. It was empty.

Spence crept into the room and as he crossed the threshold the door closed behind him. A mist came boiling out of the walls and floor, rising in a cloud before him.

Within the cloud, lightning flashed in red streaks and he could see a shape dimly emerging as if it were being knit together out of the stuff of the vapors. He watched as the shape took on human form.

Then the clouds receded, falling away in curling tendrils to reveal a creature remarkably manlike, but born of a separate creation, the child of an alien god.

He trembled in its presence as the thing, motionless, towered over him head and shoulders, its smooth, golden skin gleaming with beads of moisture. He felt a tremor pass through him as the man-being drew its first breath deep into its lungs. Spence sank to his knees before it, transfixed with awe and fear.

Then as he gazed through trembling fingers up at the stern, spare features, the eyelids flickered and raised slowly. Two great yellow eyes glared down at him and he shrank away from their terrible gaze. He threw his arms over his head and tried to hide himself from their sight.

But the being saw him, saw through him, weighed his soul with its piercing sight and found it sadly wanting. It raised one long, multijointed arm toward him and opened its wide mouth to pronounce judgment.

Spence screamed, clamping his hands over his ears… …

THE TREMOR SEEPED THROUGH the rock floor of the cavern, accompanied by a strange sighing roar. Spence, still groggy from his exhausted sleep, lay for some moments trying to remember where he was.

The rumble increased and the roar grew louder, banishing the last traces of sleep from his brain. The floor beneath him vibrated steadily. He had never stood on the slope of an active volcano, but that was the image that came to mind as he rolled up to kneel quivering with fear and uncertainty.

The thin air inside the cave convulsed as tremendous jets of water, rushing out of the sinkholes in the floor, erupted in gushers fifty meters high. The explosion knocked Spence sprawling as the floor rocked with the aftershock and tons of water rained down.

Instantly he was swept into the narrow opening of the conduit, kicking feebly against the swirling flood and slamming full force into every curve of the pipeline until he learned to relax and let the water take him.

On and on it carried him. Eventually it no longer filled the conduit; he could see a bubble forming on the roof of the tunnel. The bubble expanded until it covered a quarter of the pipe, and then half, and then it left him stranded on his stomach as it dwindled away.

He slipped off his helmet and cupped his hands to get a decent drink, but succeeded only in wetting his gloves. That, he reasoned, was better than nothing, so he held up his hands and let the water drip off his fingers into his mouth. He repeated the process several times, managing only to arouse his thirst the more for whetting it.

On hands and knees he continued his trek and arrived at the junction of a larger tunnel just as his muscles, every fiber screaming for relief, threatened to give out. This larger passageway stretched away on either hand into dark shadowy distance, slanting upward on the right and downward on the left.

He tried the upward course, but it proved too Slippery, and each attempt brought him sliding unceremoniously down a before he got a dozen paces. He decided to stop before he lost his footing altogether and went skittering into the dark corridor behind him.

He was just about to resign himself to having to take that course in any event when he spied, higher up in the tunnel wall, a small aperture he had not noticed I before. This opening suggested itself to him as an acceptable alternative and he decided to give it a try.

The decision nearly killed him.