Dave was used to being a guinea pig; that was what younger brothers were for. He adjusted his face mask, put on his flippers, and slid into the crystalline water.

Bobby handed him the air hose with the old scuba mouthpiece they had taped to it. Dave took a breath, and grimaced.

'It tastes horrible.'

'You'll get used to it. In you go – no deeper than that ledge. That's where I'll start adjusting the pressure valve so we don't waste too much air. Come up when I tug the hose.'

Dave slid gently beneath the surface, and into wonderland. It was a peaceful, monochrome world, so different from the coral reefs of the Keys. There were none of the garish colours of the marine environment, where life – animal and vegetable – flaunted itself with all the hues of the rainbow. Here were only delicate shades of blue and green, and fish that looked like fish, not like butterflies.

He flippered slowly down, dragging the hose behind him, pausing to drink from its stream of bubbles whenever he felt the need. The sensation of freedom was so wonderful that he almost forgot the horrible oily taste in his mouth. When he reached the ledge – actually an ancient, waterlogged tree trunk, so overgrown with weeds that it was unrecognizable – he sat down and looked around him.

He could see right across the spring, to the green slopes at the far side of the flooded crater, at least a hundred metres away. There were not many fish around, but a small school went twinkling past like a shower of silver coins in the sunlight streaming down from above.

There was also an old friend stationed, as usual, at the gap where the waters of the spring began their journey to the sea. A small alligator ('but large enough,' Bobby had once said cheerfully. 'He's bigger than I am.') was hanging vertically, without visible means of support, only his nose above the surface. They had never bothered him, and he had never bothered them.

The air hose gave an impatient tug. Dave was happy to go; he had not realized how cold it could get at that hitherto unattainable depth – and he was also feeling distinctly sick. But the hot sunlight soon revived his spirits.

'No problems,' said Bobby expansively. 'Just keep unscrewing the valve so the pressure gauge doesn't drop below the red line.'

'How deep are you going?'

'All the way, if I feel like it.'

Dave did not take that seriously; they both knew about rapture of the depths and nitrogen narcosis. And in any case, the old garden hose was only thirty metres long. That would be plenty for this first experiment.

As he had done so many times before, he watched with envious admiration as his beloved elder brother accepted a new challenge. Swimming as effortlessly as the fish around him, Bobby glided downward into that blue, mysterious universe. He turned once and pointed vigorously to the air hose, making it unmistakably clear that he needed an increased air flow.

Despite the splitting headache that had suddenly come upon him, Dave remembered his duty. He hurried back to the ancient compressor, and opened the control valve to its deadly maximum – fifty parts per million of carbon monoxide.

The last he saw of Bobby was that confidently descending, sunlight-dappled figure passing forever beyond his reach. The wax statue in the funeral parlour was a total stranger, who had nothing to do with Robert Bowman.

33 – Betty

Why had he come here, returning like an unquiet ghost to the scene of ancient anguish? He had no idea; indeed, he had not been conscious of his destination, until the round eye of Crystal Spring had gazed up at him from the forest below.

He was master of the world, yet he was paralysed by a sense of devastating grief he had not known for years. Time had healed the wound, as it always does; yet it seemed only yesterday that he had stood weeping beside the emerald mirror, seeing only the reflections of the surrounding cypresses with their burden of Spanish moss. What was happening to him?

And now, still without deliberate volition, but as if swept by some gentle current, he was drifting northward, toward the state capital. He was looking for something; what it was, he would not know until he found it.

No one, and no instrument, detected his passage. He was no longer radiating wastefully, but had almost mastered his control of energy, as once he had mastered lost though not forgotten limbs. He sank like a mist into the earthquakeproof vaults, until he found himself among billions of stored memories, and dazzling, flickering networks of electronic thoughts.

This task was more complex than the triggering of a crude nuclear bomb, and took him a little longer. Before he found the information he was seeking, he made one trivial slip, but did not bother to correct it. No one ever understood why, the next month, three hundred Florida taxpayers, all of whose names began with F, received cheques for precisely one dollar. It cost many times the overpayment to straighten matters out, and the baffled computer engineers finally put the blame on a cosmic-ray shower. Which, on the whole, was not so very far from the truth.

In a few milliseconds, he had moved from Tallahassee to 634 South Magnolia Street, Tampa. It was still the same address; he need not have wasted time looking it up.

But then, he had never intended to look it up, until the very moment when he had done so.

After three births and two abortions, Betty Fernandez (née Schultz) was still a beautiful woman. At the moment she was also a very thoughtful one; she was watching a TV programme that brought back memories, bitter and sweet.

It was a News Special, triggered by the mysterious events of the preceding twelve hours, beginning with the warning that Leonov had beamed back from the moons of Jupiter. Something was heading for Earth; something had – harmlessly – detonated an orbiting nuclear bomb which no one had come forward to claim. That was all, but it was quite enough.

The news commentators had dredged up all the old videotapes – and some of them really were tapes – going back to the once top-secret records showing the discovery of TMA-l on the Moon. For the fiftieth time, at least, she heard that eerie radio shriek as the monolith greeted the lunar dawn and hurled its message toward Jupiter. And once again she watched the familiar scenes and listened to the old interviews aboard Discovery.

Why was she watching? It was all stored somewhere in the home archives (though she never played it back when José was around). Perhaps she was expecting some newsflash; she did not like to admit, even to herself, how much power the past still held over her emotions.

And there was Dave, as she had expected. It was an old BBC interview, of which she knew almost every word. He was talking about Hal, trying to decide whether the computer was self-conscious or not.

How young he looked – how different from those last blurred images from the doomed Discovery! And how much like Bobby as she remembered him.

The image wavered as her eyes filled with tears. No – something was wrong with the set, or the channel. Both sound and image were behaving erratically.

Dave's lips were moving, but she could hear nothing. Then his face seemed to dissolve, to melt into blocks of colour. It reformed, blurred again, and then was steady once more. But there was still no sound.

Where had they got this picture! This was not Dave as a man, but as a boy – as she had known him first. He was looking out of the screen almost as if he could see her across the gulf of years.

He smiled; his lips moved.

'Hello, Betty,' he said.

It was not hard to form the words, and to impose them on the currents pulsing in the audio circuits. The real difficulty was to slow down his thoughts to the glacial tempo of the human brain. And then to have to wait an eternity for the answer.