There was triumph, and yet sadness, in Michaels' voice, and Floyd could share both emotions. At last, one of man's oldest questions had been answered; here was the proof, beyond all shadow of doubt, that his was not the only intelligence that the universe had brought forth. But with that knowledge there came again an aching awareness of the immensity of Time. Whatever had passed this way had missed mankind by a hundred thousand generations. Perhaps, Floyd told himself, it was just as well. And yet – what we might have learned from creatures who could cross space, while our ancestors were still living in trees!

A few hundred yards ahead, a signpost was coming up over the Moon's strangely close horizon. At its base was a tent-shaped structure covered with shining silver foil, obviously for protection against the fierce heat of day. As the bus rolled by, Floyd was able to read in the brilliant earthlight:

EMERGENCY DEPOT No. 3

20 Kilos Lox

10 Kilos Water

20 Foodpaks Mk 4

1 Toolkit Type B

1 Suit Repair Outfit

! TELEPHONE !

"Have you thought of that?" asked Floyd, pointing out of the window. "Suppose the thing's a supply cache, left behind by an expedition that never returned?"

"It's a possibility," admitted Michaels. "That magnetic field certainly labeled its position, so that it could be easily found. But it's rather small – it couldn't hold much in the way of supplies."

"Why not?" interjected Halvorsen. "Who knows bow big they were? Perhaps they were only six inches tall, which would make the thing twenty or thirty stories high."

Michaels shook his head. "Out of the question," he protested. "You can't have very small, intelligent creatures; you need a minimum brain size."

Michaels and Halvorsen, Floyd had noticed, usually took opposing viewpoints, yet there appeared to be little personal hostility or friction between them. They seemed to respect each other, and simply agreed to disagree.

There was certainly little agreement anywhere about the nature of TMA-1 – or the Tycho Monolith, as some preferred to call it, retaining part of the abbreviation.

In the six hours since he had landed on the Moon, Floyd had heard a dozen theories, but had committed himself to none. Shrine, survey marker, tomb, geophysical instrument – these were perhaps the favorite suggestions, and some of the protagonists grew very heated in their defense. A good many bets had-already been placed, and a lot of money would change hands when the truth was finally known – if, indeed, it ever was. So far, the hard black material of the slab had resisted all the rather mild attempts that Michaels and his colleagues had made to obtain samples. They had no doubt that a laser beam would cut into it – for, surely, nothing could resist that frightful concentration of energy – but the decision to employ such violent measures would be left to Floyd. He had already decided that X rays, sonic probes, neutron beams, and all other nondestructive means of investigation would be brought into play before he called up the heavy artillery of the laser. It was the mark of a barbarian to destroy something one could not understand; but perhaps men were barbarians, beside the creatures who had made this thing.

And where could they have come from? The Moon itself? No, that was utterly impossible. If there had ever been indigenous life on this barren world, it had been destroyed during the last crater-forming epoch, when most of the lunar surface was white-hot.

Earth? Very unlikely, though perhaps not quite impossible. Any advanced terrestrial civilization – presumably a nonhuman one – back in the Pleistocene Era would have left many other traces of its existence. We would have known all about it, thought Floyd, long before we got to the Moon.

That left two alternatives – the planets, and the stars.

Yet all the evidence was against intelligent life elsewhere in the Solar System – or indeed life of any kind except on Earth and Mars. The inner planets were too hot, the outer ones far too cold, unless one descended into their atmosphere to depths where the pressures amounted to hundreds of tons to the square inch.

So perhaps these visitors had come from the stars – yet that was even more incredible. As he looked up at the constellations strewn across the ebon lunar sky, Floyd remembered how often his fellow scientists had "proved" that interstellar travel was impossible. The journey from Earth to Moon was still fairly impressive, but the very nearest star was a hundred million times more distant... Speculation was a waste of time; he must wait until there was more evidence,

"Please fasten your seat belts and secure all loose objects," said the cabin speaker suddenly. "Forty degree slope approaching."

Two marker posts with winking lights had appeared on the horizon, and the bus was steering between them.

Floyd had barely adjusted his straps when the vehicle slowly edged itself over the brink of a really terrifying incline, and began to descend a long, rubble-covered slope as steep as the roof of a house. The slanting earth-light, coming from behind them, now gave very little illumination, and the bus's own floodlights had been switched on. Many years ago Floyd had stood on the lip of Vesuvius, staring into the crater; he could easily imagine that he was now driving down into it and the sensation was not a very pleasant one.

They were descending one of the inner terraces of Tycho, and it leveled out again some thousand feet below. As they crawled down the slope, Michaels pointed out across the great expanse of plain now spread out beneath them.

"There they are," he exclaimed. Floyd nodded; he had already noticed the cluster of red and green lights several miles ahead, and kept his eyes fixed upon it as the bus edged its way delicately down the slope. The big vehicle was obviously under perfect control, but he did not breathe easily until it was once more on an even keel.

Now he could see, glistening like silver bubbles in the earthlight, a group of pressure domes – the temporary shelters housing the workers on the site. Near these was a radio tower, a drilling rig, a group of parked vehicles, and a large pile of broken rock, presumably the material that had been excavated to reveal the monolith. This tiny camp in the wilderness looked very lonely, very vulnerable to the forces of nature ranged silently around it. There was no sign of life, and no visible hint as to why men had come here, so far from home.

"You can just see the crater," said Michaels. "Over there on the right – about a hundred yards from that radio antenna."

So this is it, thought Floyd, as the bus rolled past the pressure domes, and came to the lip of the crater.

His pulse quickened as he craned forward for a better view. The vehicle began to creep cautiously down a ramp of hard-packed rock, into the interior of the crater. And there, exactly as he had seen it in the photographs, was TMA-1.

Floyd stared, blinked, shook his head, and stared again. Even in the brilliant earthlight, it was hard to see the object clearly; his first impression was of a flat rectangle that might have been cut out of carbon paper; it seemed to have no thickness at all. Of course, this was an optical illusion; though he was looking at a solid body, it reflected so little light that he could see it only in silhouette.

The passengers were utterly silent as the bus descended into the crater. There was awe, and there was also incredulity – sheer disbelief that the dead Moon, of all worlds, could have sprung this fantastic surprise.

The bus came to a halt within twenty feet of the slab and broadside on so that all the passengers could examine it. Yet, beyond the geometrically perfect shape of the thing, there was little to see. Nowhere were there any marks, or any abatement of its ultimate, ebon blackness. It was the very crystallization of night, and for one moment Floyd wondered if it could indeed be some extraordinary natural formation, born of the fires and pressures attending the creation of the Moon. But that remote possibility, he knew, had already been examined and dismissed.