Rest period. His 'phones filled with the soothing resonances of music. A Bach concerto -- precise, clear, ordered notes, a wave front through his mind. His neurons triggered by each quantum of sound, electrical signals comprehended in the infinite labyrinth of his brain, firing his senses with pleasure, with pain, with memory.

"Marian, a computer can never be self-aware -- it can never live. It's a binary system. Magnetic bubbles, protein chips, whatever, it simply isn't as complex as a brain. You can't program it with all the subtle instinctive leaps of comprehension."

She turned away, as she had turned away so often in the last days. A defense, perhaps, against the memory of their baby. Their human child, vulnerable to accident, to death. "Information theory," she said impatiently, her hand on the door. "We'll be providing the construct with a grammar for learning."

"It can never be more than a machine."

"We're nothing more than molecular machines." The door opened.

He grew impatient in turn. "We're alive, Marian. And we can create new life only one way."

Her spine snapped erect, her jaw tightened, denying the agony. Wordlessly she stepped through the doorway and was gone.

And yet, David told himself, the denial was in itself agony. It used to be that men joined the Foreign Legion to forget a failed marriage; now, evidently, they volunteered for a field researcher's post on Mars. A scientist's heaven, the Noctis Labyrintius, layer upon layer of ancient rock -- the Labyrinth of Night -- the labyrinth, the place of the labrys, the double axe, reverberating to the bellows of the Minotaur -- half man, half-beast, an artificial construct -- devouring the Athenian children -- a child, a child, a child.

He started upwards, his heart pounding from the brief yet vivid nightmare. The music was over; static hissed in his ears. He flicked off the disk player, looked around at the temporarily unfamiliar shelter, calmed himself.

"Check," said Irene.

Andrei groaned. "I thought I had you foxed this time. But I'll beat you yet, honey. They couldn't have crammed that many impulses into those teeny, tiny protein chips in you mind." He extracted his king from danger.

Irene regarded the chessmen, David regarded her. Funny -- you wouldn't expect her artificial mind to change the expression of her artificial face -- why bother to program her to lower her lashes over her eyes, to smile confidently as she shifted a piece, to tap one long forefinger impatiently beside the chess board? Emotions were merely biochemical tides in the brain -- she was much better off without them.

Andrei moved, she moved again; "Checkmate," she said, and there was well-modulated triumph in her voice.

"Aargh!" Andrei exclaimed. "Too quick for me. Again tomorrow?"

In a few swift movements she cleared away the game. "Certainly. I'll go check on the culture tubes now."

Let the human guinea pigs get their ration of sleep.

Andrei stood, stretching, and realized David was watching him. "You wonder," he grinned, "why they even bothered to send us along."

Irene glanced back from the doorway. "To keep me amused," she called, perfectly deadpan.

There was something about her attitude as she moved. "Good Lord, now she's making jokes," David said quickly shrugging away his paranoia.

"She learns fast. Good night, David."

"Good night." He checked the readouts, secured the door, glanced out a dust-scummed porthole. Nothing outside. Nothing inside. In the lab Irene's movements were smooth, efficient, silent.

David lay awake a long time, brooding but he reached only the certainty that nothing was certain.

The coffee was hot; David took a quick gulp and then stood swishing it around his mouth in a futile effort to keep from burning his tongue. "Damn."

Andrei was already suiting up. "See any likely looking spots in the Labyrinth yesterday?" he called.

David returned, "Yeah. Check that gully a kilometer beyond the second marker. There seemed to be some interesting sandstone, but it was getting dark so I bailed out."

"Right."

Irene strolled through the airlock. "The empty sample containers and your tackle are in the rover."

"Thanks," Andrei told her, and with a wave of his bulkily suited arm and hand, "See you at quitting time, David."

"Keep in touch," David called after him. The coffee was a little cooler; he took another sip. The caffeine receptors in his brain were working nicely and he felt measurably more alert.

Irene was waiting. "The microbiology experiments are ready," she told him.

Reluctantly he set down the cup. His body walked into the lab; his mind followed Andrei and the rover, dwindling into a foggy peach-colored dawn. The Noctis Labyrinthus would be filled with mist, the jagged cliffs blotted into a deceptive softness, the wind still. The Labyrinth would be waiting.

All right, all right, he told himself. He bent over the readouts. Spectrometer readings were inconclusive, as usual. The Martian topsoil, with its high proportion of windblown montmorrilonite clay, absorbed and released gasses in mimicry of respiration and photosynthesis. An nice problem in inorganic chemistry, but no proof of life, microbial or otherwise.

"We'll have to refine the experiment," he told Irene, and she immediately offered several good suggestions. Work was therapeutic, David thought. He'd been thinking that a lot recently. But the problem was an interesting one, and before long he was absorbed in his task.

When he finally looked up, he was surprised at how many numbers had clicked over on the chronometer. It was long past time for Andrei to check in. Any number of things could have delayed him, David told himself. Nothing to worry about. But his shoulder blades twitched, an icicle forming along his spine.

The dark lenses of Irene's eyes dilated suddenly, and her chin went up in an unmistakable gesture of listening. Even as she moved the radio beacon let out a brief chirp.

David was on it in a moment. "Andrei?" Silence. "Andrei, are you all right?" The speaker stared back at him, mute. Hell, David thought, if he'd only tried to contact him earlier -- but that wasn't standard procedure.