The implications of his discovery sorted themselves out only gradually. Once the dimensions of his find emerged in their immensity, the finer details could be seen. The print very clearly had been made ages past counting, in order for it to have solidified into stone. If other articles of Martian civilization existed they would most likely be dust and ashes, unless fossilized.

Of course, he argued, the print need not necessarily belong to an inhabitant of Mars at all. It could just as well belong to an intruder like himself. This did not diminish his enthusiasts in the least, nor belittle his discovery. The thing was extraordinary no matter how one viewed it, but it did cause Spence to slow somewhat and consider how little he knew about the print or how it had come to be there. Clearly, he had pushed speculation beyond reasonable limits for a scientist. He would have to have many more facts to substantiate his theories, to even begin to develop any theories.

One print alone was not enough. He needed more to go on. One print alone was almost worthless. What he needed were bones, artifacts-any of the normal archaeological building blocks.

Deathly tired, his mind beginning to wander, he crossed his arms on his chest and fell asleep beside the footprint with thoughts of red Martians crawling blithely over the landscape, besmeared with chalky red dust like pygmies, and himself towering over them saying something ridiculous like, "Take me to your leader." …

THE ACHE IN HIs gut was back when he awoke, and his throat burned. A thick, gummy film had formed in his mouth, foul-tasting and nasty. His tongue felt large and uncooperative. He had heard stories of men dying of thirst in the desert, whose tongues had swelled, turning black in their mouths and choking them in the end. He wondered if this was how it started.

Grimly he got to his feet, swaying dizzily. Black spots swam before his eyes. Hunger had become a demanding force, and thirst an ever-present fire. He knew that he had little time left before he collapsed in a faint. After several such collapses he would rise no more.

He considered returning to the tunnel behind the door where the algae grew in such lush profusion. It occurred to him that he might be able to eat them and sustain himself.

The only drawback to this plan was that the algae could well be poisonous. One mouthful could cause him to end his life retching out his entrails in a cold sweat, or send him screaming in agony to crush his head against the stones to stop the pain. These were the milder scenarios he imagined-less pleasant possibilities occurred to him which he did not care to entertain.

Spence decided that if he had found no water by the time he slept once more he would return to the passage beyond the stone door-he now considered it a door in every sense of the word-and eat the algae, come what may. He would by that time be on his last strength and it would not matter which way his life finally ceased. At that point he would be willing to gamble, but not before.

So, he lurched off once more, climbing up the passageway. Not more than a few meters up, the tunnel ended and he stepped into a vast underground cavity of enormous proportions. He began walking, head down, shoulders forward, arms swinging loosely at his sides.

Soon he was pleased to discover that his gnawing hunger had eased. He felt clean, lean, purged of a heaviness that weighed on his body and spirit, electrically alive.

Spence knew this to be the sensation associated with a fast. Medically, the effect was well recognized. Still, he could not help feeling the intense emotional impact of the phenomenon. He felt, for lack of a better word, spiritual.

At intervals along the route-he decided to move directly ahead, keeping the tunnel at his back-thick columns of stone rose from the floor like the trunks of trees. He wondered at these but they, like the slab door, seemed to be natural formations such as one might find in any cave. There was no reason to believe they were not exotic forms of stalagmites peculiar to the Martian lithosphere.

And yet the sprout of suspicion had already woven its snaking fibrils deep into his consciousness. What if they, like the footprint, were not natural?

The implications were too extraordinary to entertain for any length of time. But increasingly the suggestion of trespassing occurred to him. How he had struck upon that particular word he could not say, but it seemed appropriate.

He felt like one trespassing on private ground. A grave – robber desecrating a pharaoh's tomb. He imagined that at any moment a whole phalanx of spear-toting soldiers would come swinging into view from behind one of those strange columns. He had visions of plumed horses and chariots dragging him through the village square while the screaming alien populace jeered, "Thief! Grave-robber! Desecrater!"

These daydreams he knew to be associated with his deprivation. He had begun to feel his thirst once more-the tiny amount of water he had scooped from the conduit floor was not enough to sustain him. He needed a real drink badly.

He hoped that the flood which had washed him through the tunnel could be located again. There was water on Mars; maybe not much, but it existed. He had navigated it; finding it again was a project becoming uppermost in his mind.

Gradually, as he walked along the dull red cavern floor, listening to his own footsteps pattering away into the darkness, the roof of the cave sloped away and with it the rust-colored lichen clinging to its surface. The lichen, he discovered, gave off a pale aura like the algae in the tunnels.

He made his way along through a dim and hazy light of ruddy gold which reached him as sunlight through the flaming canopy of autumn trees. But here the trees were stone and no leaves scattered before his feet.

He fell into an easy rhythm of walking, trying to maintain asteady course forward. The tempo of his steps carried him along.After a few hours of walking he slept again, and then oncemore after that-still unwilling to give in and return to the tunnel and the algae. Each time he slept less and woke less rested than before. He supposed this to be the effect of his fast. His body was beginning to turn on itself for nourishment. He felt lightheaded, airy, spiritlike, pure.

In his journey through the Martian underground Spence's eyes turned inward and he gazed upon his life with the kind of aloof objectivity he usually reserved for his work, with the same meticulous scrutiny and the same relentless curiosity. Only this time the subject was himself.

Though considered a fast-rising star by most, he nevertheless knew himself to have fallen far short of the mark. There were others he knew who had accomplished more, received higher praise, garnered more of the glittering prizes he sought, whose names were better known and respected more than his own. The resent ment he felt for those fortunate others had hardened into a burning, almost ruthless ambition to surmount their achievements an ambition Spence had always prided himself on, thinking it a virtue and a means to his personal fulfillment.

Now, considering his circumstances and the shallowness of his inner being, he viewed that ambition for what it was-a flame which had consumed nearly all his better qualities to fuel itself. Compassion, generosity, joy, even love-these had been given to the fire and it had all but consumed them. And now what had he to show for his pains?

Nothing of lasting value. Nothing that would live after him. All had been directed inward, feeding the flame. That he had any redeeming qualities left at all seemed to him something of a miracle, so much had been given to the all-consuming fire.

In this delicate, suggestible state he felt the loss of all those years of determined self-denial-the endless studying, working, striving. The waste appalled him.