A flickering blue lake had opened up near the equator; he was sure it had not been there a few hours earlier. Brilliant yellow flares, the characteristic colour of glowing sodium, were dancing along its edges; and the whole of the nightland was veiled in the ghostly plasma discharge of one of Io's almost continuous auroras.

It was the stuff of future nightmares – and as if that was not sufficient, there was one further touch worthy of a mad surrealist artist. Stabbing up into the black sky, apparently emerging directly from the firepits of the burning moon, was an immense, curving horn, such as a doomed bullfighter might have glimpsed in the final moment of truth.

The crescent of Jupiter was rising to greet Discovery and Leonov as they swept toward it along their common orbit.

The moment that the outer hatch had closed behind them, there had been a subtle reversal of roles. Curnow was at home now, while Brailovsky was out of his element, feeling ill at ease in the labyrinth of pitch-black corridors and tunnels that was Discovery's interior. In theory, Max knew his way round the ship, but that knowledge was based only on a study of its design drawings. Curnow, on the other hand, had spent months working in Discovery's still uncompleted identical twin; he could, quite literally, find his way around blindfolded.

Progress was made difficult because that part of the ship was designed for zero gee; now the uncontrolled spin provided an artificial gravity, which, slight though it was, always seemed to be in the most inconvenient direction.

'First thing we've got to do,' muttered Curnow, after sliding several metres down a corridor before he could grab a handhold, 'is to stop this damned spin. And we can't do that until we have power. I only hope that Dave Bowman safeguarded all systems before he abandoned ship.'

'Are you sure he did abandon the ship? He may have intended to come back.'

'You may be right; I don't suppose we'll ever know. If he even knew himself.'

They had now entered the Pod Bay – Discovery's 'space garage', which normally contained three of the spherical one-man modules used for activities outside the ship. Only Pod Number 3 remained; Number 1 had been lost in the mysterious accident that had killed Frank Poole – and Number 2 was with Dave Bowman, wherever he might be.

The Pod Bay also contained two spacesuits, looking uncomfortably like decapitated corpses as they hung helmet-less in their racks. It needed very little effort of the imagination – and Brailovsky's was now working overtime – to fill them with a whole menagerie of sinister occupants.

It was unfortunate, but not altogether surprising, that Curnow's sometimes irresponsible sense of humour got the better of him at this very moment.

'Max,' he said, in a tone of deadly seriousness, 'whatever happens – please don't go chasing off after the ship's cat.'

For a few milliseconds, Brailovsky was thrown off guard; he almost answered: 'I do wish you hadn't said that, Walter', but checked himself in time. That would have been too damning an admission of weakness; instead he replied, 'I'd like to meet the idiot who put that movie in our library.'

'Katerina probably did it, to test everyone's psychological balance. Anyway, you laughed your head off when we screened it last week.'

Brailovsky was silent; Curnow's remark was perfectly true. But that had been back in the familiar warmth and light of Leonov, among his friends – not in a pitch-black, freezing derelict, haunted by ghosts. No matter how rational one was, it was all too easy to imagine some implacable alien beast prowling these corridors, seeking whom it might devour.

It's all your fault, Grandma (may the Siberian tundra lie lightly on your beloved bones) – I wish you hadn't filled my mind with so many of those gruesome legends. If I close my eyes, I can still see the hut of the Baba Yaga, standing in that forest clearing on its scrawny chicken legs...

Enough of this nonsense. I'm a brilliant young engineer faced with the biggest technical challenge of his life, and I mustn't let my American friend know that I'm sometimes a frightened little boy.

The noises did not help. There were too many of them, though they were so faint that only an experienced astronaut would have detected them against the sounds of his own suit. But to Max Brailovsky, accustomed to working in an environment of utter silence, they were distinctly unnerving, even though he knew that the occasional cracklings and creakings were almost certainly caused by thermal expansion as the ship turned like a roast on a spit. Feeble though the sun was out here, there was still an appreciable temperature change between light and shade.

Even his familiar spacesuit felt wrong, now that there was pressure outside as well as in. All the forces acting on its joints were subtly altered, and he could no longer judge his movements accurately. I'm a beginner, starting my training all over again, he told himself angrily. Time to break the mood by some decisive action.

'Walter – I'd like to test the atmosphere.'

'Pressure's okay; temperature – phew – it's one hundred five below zero.'

'A nice bracing Russian winter. Anyway, the air in my suit will keep out the worst of the cold.'

'Well, go ahead. But let me shine my light on your face, so I can see if you start to turn blue. And keep talking.'

Brailovsky unsealed his visor and swung the faceplate upward. He flinched momentarily as icy fingers seemed to caress his cheeks, then took a cautious sniff, followed by a deeper breath.

'Chilly – but my lungs aren't freezing. There's a funny smell, though. Stale, rotten – as if something's – oh no!'

Looking suddenly pale, Brailovsky quickly snapped the faceplate shut.

'What's the trouble, Max?' Curnow asked with sudden and now perfectly genuine anxiety. Brailovsky did not reply; he looked as if he was still trying to regain control of himself. Indeed, he seemed in real danger of that always horrible and sometimes fatal disaster – vomiting in a spacesuit.

There was a long silence; then Curnow said reassuringly:

'I get it. But I'm sure you're wrong. We know that Poole was lost in space. Bowman reported that he... ejected the others after they died in hibernation – and we can be sure that he did. There can't be anyone here. Besides, it's so cold.' He almost added 'like a morgue' but checked himself in time.

'But' suppose,' whispered Brailovsky, 'just suppose Bowman managed to get back to the ship – and died here.'

There was an even longer silence before Curnow deliberately and slowly opened his own faceplate. He winced as the freezing air bit into his lungs, then wrinkled his nose in disgust.

'I see what you mean. But you're letting your imagination run away with you. I'll bet you ten to one that smell comes from the galley. Probably some meat went bad, before the ship froze up. And Bowman must have been too busy to be a good housekeeper. I've known bachelor apartments that smelled as bad as this.'

'Maybe you're right. I hope you are.'

'Of course I am. And even if I'm not – dammit, what difference does it make? We've got a job to do, Max. If Dave Bowman's still here, that's not our department – is it, Katerina?'

There was no reply from the Surgeon-Commander; they had gone too far inside the ship for radio to penetrate. They were indeed on their own, but Max's spirits were rapidly reviving. It was a privilege, he decided, to work with Walter. The American engineer sometimes appeared soft and easygoing. But he was totally competent – and, when necessary, as hard as nails.

Together, they would bring Discovery back to life; and, perhaps, back to Earth.