I'll wait until time zero – no, it's not that critical, let's say an extra minute – then I'll zap him and we'll go over to manual...

From far, far away there came a faint, whistling scream, like the sound of a tornado marching just below the edge of the horizon. Discovery started to vibrate; there was the first intimation of returning gravity.

'Ignition,' said Hal. 'Full thrust at T plus fifteen seconds.'

'Thank ,you, Hal,' replied Chandra.

48 – Over the Nightside

To Heywood Floyd, aboard the suddenly unfamiliar – because no longer weightless – environment of Leonov's flight deck, the sequence of events had seemed more like a classic slow-motion nightmare than reality. Only once before in his life had he known a similar situation, when he had been in the back of a car during an uncontrollable skid. There had been that same sense of utter helplessness – coupled with the thought: This doesn't really matter – it's not actually happening to me.

Now that the firing sequence had started, his mood changed; everything seemed real again. It was working out exactly as they had planned; Hal was guiding them safely back to Earth. With every minute that passed, their future was becoming more secure; Floyd began slowly to relax, even though he remained alert to all that was happening around him.

For the very last time – and when would any man come here again? – he was flying over the nightside of the greatest of planets, encompassing the volume of a thousand Earths. The ships had been rolled so that Leonov was between Discovery and Jupiter, and their view of the mysteriously glimmering cloudscape was not blocked. Even now, dozens of instruments were busily probing and recording; Hal would continue the work when they were gone.

Since the immediate crisis was over, Floyd moved cautiously 'down' from the flight deck-how strange to feel weight again, even if it was only ten kilos! – and joined Zenia and Katerina in the observation lounge. Apart from the very faintest of red emergency lights, it had been completely blacked out so that they could admire the view with unimpaired night vision. He felt sorry for Max Brailovsky and Sasha Kovalev, who were sitting in the airlock, fully suited up, missing the marvellous spectacle. They had to be ready to leave at a moment's notice to cut the straps securing the ships together – if any of the explosive charges failed to operate.

Jupiter filled the entire sky; it was a mere five hundred kilometres away, so they could see only a tiny fraction of its surface – no more than one could see of Earth from an altitude of fifty kilometres. As his eyes grew accustomed to the dim light, most of it reflected from the icy crust of distant Europa, Floyd could make out a surprising amount of detail. There was no colour at the low level of illumination – except for a hint of red here and there – but the banded structure of the clouds was very distinct, and he could see the edge of a small cyclonic storm looking like an oval island covered with snow. The Great Black Spot had long since fallen astern, and they would not see it again until they were well on the way home.

Down there beneath the clouds, occasional explosions of light flared, many of them obviously caused by the Jovian equivalent of thunderstorms. But other glows and outbursts of luminescence were more long-lived, and of more uncertain origin. Sometimes rings of light would spread out like shock waves from a central source; and occasional rotating beams and fans occurred. It required little imagination to pretend that they were proof of a technological civilization down beneath those clouds – the lights of cities, the beacons of airports. But radar and balloon probes had long ago proved that nothing solid was down there for thousands upon thousands of kilometres, all the way to the unattainable core of the planet.

Midnight on Jupiter! The last close-up glimpse was a magical interlude he would remember all his life. He could enjoy it all the more because, surely, nothing could now go wrong; and even if it did, he would have no reason to reproach himself He had done everything possible to ensure success.

It was very quiet in the lounge; no one wished to speak as the carpet of clouds unrolled swiftly beneath them. Every few minutes Tanya or Vasili announced the status of the burn; toward the end of Discovery's firing time, tension began to increase again. This was the critical moment – and no one knew exactly when it would be. There was some doubt as to the accuracy of the fuel gauges, and the burn would continue until they were completely dry.

'Estimated cut-off in ten seconds,' said Tanya. 'Walter, Chandra – get ready to come back. Max, Vasili – stand by in case you're needed. Five... four... three... two... one... zero!'

There was no change; the faint scream of Discovery's engines still reached them through the thickness of the two hulls, and the thrust-induced weight still continued to grip their limbs. We're in luck, thought Floyd; the gauges must have been reading low, after all. Every second of extra firing was a bonus; it might even mean the difference between life and death. And how strange to hear a countup instead of a countdown!

five seconds... ten seconds... thirteen seconds. That's it – lucky thirteen!'

Weightlessness, and silence, returned. On both ships, there was a brief burst of cheering. It was quickly truncated, for much was still to be done – and it had to be done swiftly.

Floyd was tempted to go to the airlock so that he could give his congratulations to Chandra and Curnow as soon as they came aboard. But he would only be in the way; the airlock would be a very busy place as Max and Sasha prepared for their possible EVA and the tubeway joining the two ships was disconnected. He would wait in the lounge, to greet the returning heroes.

And he could now relax even further – perhaps from eight to seven, on a scale of ten. For the first time in weeks, he could forget about the radio cut-off. It would never be needed; Hal had performed impeccably. Even if he wished, he could do nothing to affect the mission since Discovery's last drop of propellant had been exhausted.

'All aboard,' announced Sasha. 'Hatches sealed. I'm going to fire the charges.'

There was not the faintest sound as the explosives were detonated, which surprised Floyd; he had expected some noise to be transmitted through the straps, taut as steel bands, that linked the ships together. But there was no doubt that they had gone off as planned, for Leonov gave a series of tiny shudders, as if someone was tapping on the hull. A minute later, Vasili triggered the attitude jets for a single brief burst.

'We're free!' he shouted. 'Sasha, Max – you won't be needed! Everyone get to your hammocks – ignition in one hundred seconds!'

And now Jupiter was rolling away, and a strange new shape appeared outside the window – the long, skeletal frame of Discovery, navigation lights still shining as it drifted away from them and into history. No time remained for sentimental farewells; in less than a minute Leonov's drive would start to operate.

Floyd had never heard it under full power and wanted to protect his ears from the roaring scream that now filled the universe. Leonov's designers had not wasted payload on sound-insulation that would be needed for only a few hours of a voyage that would last for years. And his weight seemed enormous – yet it was barely a quarter of that which he had known all his life.

Within minutes, Discovery had vanished astern, though the flash of its warning beacon could be seen until it had dropped below the horizon. Once again, Floyd told himself, I'm rounding Jupiter – this time gaining speed, not losing it. He glanced across at Zenia, just visible in the darkness with her nose pressed to the observation window. Was she also recalling that last occasion, when they shared the hammock together? There was no danger of incineration now; at least she would not be terrified of that particular fate. Anyway, she seemed a much more confident and cheerful person, undoubtedly thanks to Max – and perhaps Walter as well.