Tanya was speaking over the intercom; her words were lost in the roar, but her voice sounded calm and perfectly normal, just as if she was making a routine announcement. Floyd managed to glance at his watch, and was astonished to see that they were already at the midpoint of the braking manoeuvre. At that very moment, Leonov was at its closest approach to Jupiter; only expendable automatic probes had gone deeper into the Jovian atmosphere.

'Halfway through, Zenia,' he shouted. 'On the way out again.' He could not tell if she understood. Her eyes were tightly closed, but she smiled slightly.

The ship was now rocking noticeably, like a small boat in a choppy sea. Was that normal? wondered Floyd. He was glad that he had Zenia to worry about; it took his mind away from his own fears. Just for a moment, before he managed to expel the thought, he had a vision of the walls suddenly glowing cherry red, and caving in upon him. Like the nightmare fantasy of Edgar Allan Poe's 'The Pit and the Pendulum', which he'd forgotten for thirty years.

But that would never happen. If the heat shield failed, the ship would crumble instantly, hammered flat by a solid wall of gas. There would be no pain; his nervous system would not have time to react before it ceased to exist. He had experienced more consoling thoughts, but this one was not to be despised.

The buffeting slowly weakened. There was another inaudible announcement from Tanya (he would pull her leg about that, when it was all over). Now time seemed to be going much more slowly; after a while he stopped looking at his watch, because he could not believe it. The digits changed so slowly that he could almost imagine himself in some Einsteinian time dilation.

And then something even more unbelievable happened. First he was amused, then slightly indignant. Zenia had fallen asleep – if not exactly in his arms, then at least beside them.

It was a natural reaction: the strain must have exhausted her, and the wisdom of the body had come to her rescue. And suddenly Floyd himself became aware of an almost post-orgasmic drowsiness, as if he too had been emotionally drained by the encounter. He had to fight to remain awake.

And then he was falling... falling... falling... it was all over. The ship was back in space, where it belonged. And he and Zenia were floating apart.

They would never again be so close together, but they would always know a special tenderness toward each other, which no one else could ever share.

When Floyd reached the observation deck – a discreet few minutes after Zenia – Jupiter already seemed farther away. But that must be an illusion based on his knowledge, not the evidence of his eyes. They had barely emerged from the Jovian atmosphere, and the planet still filled half the sky.

And now they were – as intended – its prisoners. During the last incandescent hour, they had deliberately jettisoned the excess speed that could have carried them right out of the Solar System, and on to the stars. Now they were travelling in an ellipse – a classical Hohmann orbit – which would shuttle them back between Jupiter and the orbit of Io, 350,000 kilometres higher. If they did not – or could not – fire their motors again, Leonov would swing back and forth between these limits, completing one revolution every nineteen hours. It would become the closest of Jupiter's moons – though not for long. Each time it grazed the atmosphere it would lose altitude, until it spiralled into destruction.

Floyd had never really enjoyed vodka, but he joined the others without any reservations in drinking a triumphant toast to the ship's designers, coupled with a vote of thanks to Sir Isaac Newton. Then Tanya put the bottle firmly back in its cupboard; there was still much to be done.

Though they were all expecting it, everyone jumped at the sudden muffled thud of explosive charges, and the jolt of separation. A few seconds later, a large, still-glowing disk floated into view, slowly turning end-over-end as it drifted away from the ship.

'Look!' cried Max. 'A flying saucer! Who's got a camera?' There was a distinct note of hysterical relief in the laughter that followed. It was interrupted by the captain, in a more serious vein.

'Goodbye, faithful heat shield! You did a wonderful job.'

'But what a waste!' said Sasha. 'There's at least a couple of tons left, Think of all the extra payload we could have carried!'

'If that's good, conservative Russian engineering,' retorted Floyd, 'then I'm all for it. Far better a few tons too much – than one milligram too little.'

Everyone applauded those noble sentiments as the jetti soned shield cooled to yellow, then red, and finally became as black as the space around it. It vanished from sight while only a few kilometres away, though occasionally the sudden reappearance of an eclipsed star would betray its presence.

'Preliminary orbit check completed,' said Vasili. 'We're within ten metres a second of our right vector. Not bad for a first try.'

There was a subdued sigh of relief at the news, and a few minutes later Vasili made another announcement.

'Changing attitude for course correction; delta vee six metres a second. Twenty-second burn coming up in one minute.'

They were still so close to Jupiter it was impossible to believe that the ship was orbiting the planet; they might have been in a high-flying aircraft that had just emerged from a sea of clouds. There was no sense of scale; it was easy to imagine that they were speeding away from some terrestrial sunset; the reds and pinks and crimsons sliding below were so familiar.

And that was an illusion; nothing here had any parallels with Earth. Those colours were intrinsic, not borrowed from the setting sun. The very gases were utterly alien – methane and ammonia and a witch's brew of hydrocarbons, stirred in a hydrogen-helium cauldron. Not one trace of free oxygen, the breath of human life.

The clouds marched from horizon to horizon in parallel rows, distorted by occasional swirls and eddies. Here and there upwellings of brighter gas broke the pattern, and Floyd could also see the dark rim of a great whirlpool, a maelstrom of gas leading down into unfathomable Jovian depths.

He began to look for the Great Red Spot, then quickly checked himself at such a foolish thought. All the enormous cloudscape he could see below would be only a few per cent of the Red Spot's immensity; one might as well expect to recognize the shape of the United States from a small aeroplane flying low above Kansas.

'Correction completed. We're now on interception orbit with Io. Arrival time: eight hours, fifty-five minutes.'

Less than nine hours to climb up from Jupiter and meet whatever is waiting for us, thought Floyd. We've escaped from the giant – but he represents a danger we understood, and could prepare for. What lies ahead now is utter mystery.

And when we have survived that challenge, we must return to Jupiter once again. We shall need his strength to send us safely home.