"Whether the civilization which set it up still exists, we do not know. We must assume that creatures whose machines still function after three million years may build a society equally long-lasting. And we must also assume, until we have evidence to the contrary, that they may be hostile. It has often been argued that any advanced culture must be benevolent, but we cannot take any chances.

"Moreover, as the past history of our own world has shown so many times, primitive races have often failed to survive the encounter with higher civilizations. Anthropologists talk of 'cultural shock'; we may have to prepare the entire human race for such a shock. But until we know something about the creatures who visited the Moon – and presumably the Earth as well – three million years ago, we cannot even begin to make any preparations.

"Your mission, therefore, is much more than a voyage of discovery. It is a scouting trip – a reconnaissance into unknown and potentially dangerous territory. The team under Dr. Kaminski had been specially trained for this work; now you will have to manage without them.

"Finally – your specific target. It seems incredible that advanced forms of life can exist on Saturn, or could ever have evolved on any of its moons. We had planned to survey the entire system, and we still hope that you can carry out a simplified program. But now we may have to concentrate on the eighth satellite – Japetus. When the time comes for the terminal maneuver, we will decide whether you should rendezvous with this remarkable object.

"Japetus is unique in the Solar System – you know this already, of course, but like all the astronomers of the last three hundred years, you've probably given it little thought. So let me remind you that Cassini – who discovered Japetus in 1671 – also observed that it was six times brighter on one side of its orbit than the other.

"This is an extraordinary ratio, and there has never been a satisfactory explanation for it. Japetus is so small – about eight hundred miles in diameter – that even in the lunar telescopes its disk is barely visible. But there seems to be a brilliant, curiously symmetrical spot on one face, and this may be connected with TMA-1. I sometimes think that Japetus has been flashing at us like a cosmic heliograph for three hundred years, and we've been too stupid to understand its message.

"So now you know your real objective, and can appreciate the vital importance of this mission. We are all praying that you can still provide us with some facts for a preliminary announcement; the secret cannot be kept indefinitely.

"At the moment, we do not know whether to hope or fear. We do not know if, out on the moons of Saturn, you will meet with good or with evil – or only with ruins a thousand times older than Troy."

Work is the best remedy for any shock, and Bowman now had work enough for all his lost crewmates. As swiftly as possible, starting with the vital systems without which he and the ship would die, he had to get Discovery fully operational again.

Life support was the first priority. Much oxygen had been lost, but the reserves were still ample to sustain a single man. The pressure and temperature regulation was largely automatic, and there had seldom been need for Hal to interfere with it. The monitors on Earth could now carry out many of the higher duties of the slain computer, despite the long time lag before they could react to changing situations. Any trouble in the life-support system – short of a serious puncture in the hull – would take hours to make itself apparent; there would be plenty of warning.

The ship's power, navigation, and propulsion systems were unaffected – but the last two, in any event, Bowman would not need for months, until it was time to rendezvous with Saturn. Even at long range, without the help of an onboard computer, Earth could still supervise this operation. The final orbit adjustments would be somewhat tedious, because of the constant need for checking, but this was no serious problem.

By far the worst job had been emptying the spinning coffins in the centrifuge. It was well, Bowman thought thankfully, that the members of the survey team had been colleagues, but not intimate friends. They had trained together for only a few weeks; looking back on it, he now realized that even this had been largely a compatibility test.

When he had finally sealed the empty hibernacula, he felt rather like an Egyptian tomb robber. Now Kaminski, Whitehead, and Hunter would all reach Saturn before him – but not before Frank Poole. Somehow, he derived a strange, wry satisfaction from this thought.

He did not attempt to find if the rest of the hibernation system was still in working order. Though his life might ultimately depend upon it, this was a problem that could wait until the ship had entered its final orbit. Many things might happen before then.

It was even possible – though he had not yet looked into the supply position carefully – that by rigorous rationing he might remain alive, without resort to hibernation, until rescue came. But whether he could survive psychologically as well as physically was quite another matter.

He tried to avoid thinking about such long-range problems, and to concentrate on immediate essentials. Slowly, he cleaned up the ship, checked that its systems were still running smoothly, discussed technical difficulties with Earth, and operated on the minimum of sleep. Only at intervals, during the first weeks, was he able to give much thought to the great mystery toward which he was now inexorably racing – though it was never very far from his mind.

At last, as the ship slowly settled down once more into an automatic routine – though one that still demanded his constant supervision – Bowman had time to study the reports and briefings sent to him from Earth. Again and again he played back the recording made when TMA-1 greeted the dawn for the first time in three million years. He watched the spacesuited figures moving around it, and almost smiled at their ludicrous panic when it blasted its signal at the stars, paralyzing their radios with the sheer power of its electronic voice.

Since that moment, the black slab had done nothing. It had been covered up, then cautiously exposed to the Sun again – without any reaction. No attempt had been made to cut into it, partly through scientific caution, but equally through fear of the possible consequences.

The magnetic field that led to its discovery had vanished at the moment of that radio shriek. Perhaps, some experts theorized, it had been generated by a tremendous circulating current, flowing in a superconductor and thus carrying energy down the ages until it was needed. That the monolith had some internal source of power seemed certain; the solar energy it had absorbed during its brief exposure could not account for the strength of its signal.

One curious, and perhaps quite unimportant, feature of the block had led to endless argument The monolith was 11 feet high, and 11/4 by 5 feet in cross-section. When its dimensions were checked with great care, they were found to be in the exact ratio 1 to 4 to 9 – the squares of the first three integers. No one could suggest any plausible explanation for this, but it could hardly be a coincidence, for the proportions held to the limits of measurable accuracy. It was a chastening thought that the entire technology of Earth could not shape even an inert block, of any material, with such a fantastic degree of precision. In its way, this passive yet almost arrogant display of geometrical perfection was as impressive as any of TMA-l's other attributes.

Bowman also listened, with a curiously detached interest, to Mission Control's belated apologia for its programming. The voices from Earth seemed to have a defensive note; be could imagine the recriminations that must now be in progress among those who had planned the expedition.