At some signal, floodlights around the lip of the crater were switched on, and the bright earthlight was obliterated by a far more brilliant glare. In the lunar vacuum the beams were, of course, completely invisible; they formed overlapping ellipses of blinding white, centered on the monolith. And where they touched it, its ebon surface seemed to swallow them.

Pandora's box, thought Floyd, with a sudden sense of foreboding – waiting to be opened by inquisitive Man.

And what will he find inside?

The main pressure dome at the TMA-1 site was only twenty feet across, and its interior was uncomfortably crowded. The bus, coupled to it through one of the two airlocks, gave some much-appreciated extra living room.

Inside this hemispherical, double-walled balloon lived, worked, and slept the six scientists and technicians now permanently attached to the project. It also contained most of their equipment and instruments, all the stores that could not be left in the vacuum outside, cooking, washing, and toilet facilities, geological samples and a small TV screen through which the site could be kept under continuous surveillance.

Floyd was not surprised when Halvorsen elected to remain in the dome; he stated his views with admirable frankness.

"I regard spacesuits as a necessary evil," said the Administrator, "I wear one four times a year, for my quarterly checkout tests. If you don't mind, I'll sit here and watch over the TV."

Some of this prejudice was now unjustified, for the latest models were infinitely more comfortable than the clumsy suits of armor worn by the first lunar explorers. They could be put on in less than a minute, even without help, and were quite automatic. The Mk V into which Floyd was now carefully sealed would protect him from the worst that the Moon could do, either by day or by night.

Accompanied by Dr. Michaels, he walked into the small airlock. As the throbbing of the pumps died away, and his suit stiffened almost imperceptibly around him, he felt himself enclosed in the silence of vacuum.

That silence was broken by the welcome sound of his suit radio.

"Pressure O.K., Dr. Floyd? Are you breathing normally?"

"Yes – I'm fine."

His companion carefully checked the dials and gauges on the outside of Floyd's suit. Then he said:

"O.K.-let's go."

The outer door opened, and the dusty moonscape lay before them, glimmering in the earthlight.

With a cautious, waddling movement, Floyd followed Michaels through the lock. It was not hard to walk; indeed, in a paradoxical way the suit made him feel more at home than at any time since reaching the Moon. Its extra weight, and the slight resistance it imposed on his motion, gave some of the illusion of the lost terrestrial gravity.

The scene had changed since the party had arrived barely an hour ago. Though the stars, and the half-earth, were still as bright as ever, the fourteen-day lunar night had almost ended. The glow of the corona was like a false moonrise along the eastern sky – and then, without warning, the tip of the radio mast a hundred feet above Floyd's head suddenly seemed to burst into flame, as it caught the first rays of the hidden sun.

They waited while the project supervisor and two of his assistants emerged from the airlock, then walked slowly toward the crater. By the time they had reached it, a thin bow of unbearable incandescence had thrust itself above the eastern horizon. Though it would take more than an hour for the sun to clear the edge of the slowly turning moon, the stars were already banished. The crater was still in shadow, but the floodlights mounted around its rim lit the interior brilliantly. As Floyd walked slowly down the ramp toward the black rectangle, he felt a sense not only of awe but of helplessness. Here, at the very portals of Earth, man was already face to face with a mystery that might never be solved. Three million years ago, something had passed this way, had left this unknown and perhaps unknowable symbol of its-purpose, and had returned to the planets – or to the stars.

Floyd's suit radio interrupted his reverie. "Project supervisor speaking. If you'd all line up on this side, we'd like to take a few photos. Dr. Floyd, will you stand in the middle – Dr. Michaels – thank you. No one except Floyd seemed to think that there was anything funny about this. In all honesty, he had to admit that he was glad someone had brought a camera; here was a photo that would undoubtedly be historic, and he wanted copies for himself. He hoped that his face would be clearly visible through the helmet of the suit.

"Thanks, gentlemen," said the photographer, after they had posed somewhat self-consciously in front of the monolith, and he had made a dozen exposures.

"We'll ask the Base Photo Section to send you copies." Then Floyd turned his full attention to the ebon slab – walking slowly around it, examining it from every angle, trying to imprint its strangeness upon his mind.

He did not expect to find anything, for he knew that every square inch had already been gone over with microscopic care.

Now the sluggish sun had lifted itself above the edge of the crater, and its rays were pouring almost broadside upon the eastern face of the block. Yet it seemed to absorb every particle of light as if it had never been.

Floyd decided to try a simple experiment; he stood between the monolith and the sun, and looked for his own shadow on the smooth black sheet. There was no trace of it. At least ten kilowatts of raw heat must be falling on the slab; if there was anything inside, it must be rapidly cooking.

How strange, Floyd thought, to stand here while – this thing – is seeing daylight for the first time since the Ice Ages began on Earth. He wondered again about its black color; that was ideal, of course, for absorbing solar energy. But he dismissed the thought at once; for who would be crazy enough to bury a sunpowered device twenty feet underground?

He looked up at the Earth, beginning to wane in the morning sky. Only a handful of the six billion people there knew of this discovery; how would the world react to the news when it was finally released? The political and social implications were immense; every person of real intelligence – everyone who looked an inch beyond his nose – would find his life, his values, his philosophy, subtly changed. Even if nothing whatsoever was discovered about TMA-1, and it remained an eternal mystery, Man would know that he was not unique in the universe. Though he had missed them by millions of years, those who had once stood here might yet return: and if not, there might well be others. All futures must now contain this possibility.

Floyd was still musing over these thoughts when his helmet speaker suddenly emitted a piercing electronic shriek, like a hideously overloaded and distorted time signal. Involuntarily, he tried to block his ears with his spacesuited hands; then he recovered and groped frantically for the gain control of his receiver. While he was still fumbling four more of the shrieks blasted out of the ether; then there was a merciful silence.

All around the crater, figures were standing in attitudes of paralyzed astonishment. So it's nothing wrong with my gear, Floyd told himself; everyone heard those piercing electronic screams.

After three million years of darkness, TMA-1 had greeted the lunar dawn.