'You must be making a joke. Can you imagine them doing that? They're much too proud. Anyway, it would be impossible. We can't change our mission profile, as you know perfectly well. Even if we had the fuel...'

'You're right, of course; but it might be difficult to explain that to the ninety-nine per cent of the human race that doesn't understand orbital mechanics. We should start thinking about some of the political complications – it would look bad for all of us if we can't help. Vasili, will you give me their final orbit, as soon as you've worked it out? I'm going down to my cabin to do some homework.'

Floyd's cabin, or rather one-third of a cabin, was still partly full of stores, many of them stacked in the curtained bunks that would be occupied by Chandra and Curnow when they emerged from their long slumbers. He had managed to clear a small working space for his personal effects and had been promised the luxury of another whole two cubic metres – just as soon as someone could be spared to help with the furniture removing.

Floyd unlocked his little communications console, set the decryption keys, and called for the information on Tsien that had been transmitted to him from Washington. He wondered if his hosts had had any luck in unscrambling it; the cipher was based on the product of two hundred-digit prime numbers, and the National Security Agency had staked its reputation on the claim that the fastest computer in existence could not crack it before the Big Crunch at the end of the Universe. It was a claim that could never be proved – only disproved.

Once again he stared intently at the excellent photographs of the Chinese ship, taken when it had revealed its true colours and was just about to leave Earth orbit. There were later shots – not so clear, because by then it had been far away from the prying cameras – of the final stage as it hurtled toward Jupiter. Those were the ones that interested him most; even more useful were the cutaway drawings and estimates of performance.

Granted the most optimistic assumptions, it was difficult to see what the Chinese hoped to do. They must have burned up at least ninety per cent of their propellant in that mad dash across the Solar System. Unless it was literally a suicide mission – something that could not be ruled out – only a plan involving hibernation and later rescue made any sense. And Intelligence did not believe that Chinese hibernation technology was sufficiently far advanced to make that a viable option.

But Intelligence was frequently wrong, and even more often confused by the avalanche of raw facts it had to evaluate – the 'noise' in its information circuits. It had done a remarkable job on Tsien, considering the shortness of time, but Floyd wished that the material sent to him had been more carefully filtered. Some of it was obvious junk, of no possible connection with the mission.

Nevertheless, when you did not know what you were looking for, it was important to avoid all prejudices and preconceptions; something that at first sight seemed irrelevant, or even nonsensical, might turn out to be a vital clue.

With a sigh, Floyd started once more to skim the five hundred pages of data, keeping his mind as blankly receptive as possible while diagrams, charts, photographs – some so smudgy that they could represent almost anything – news items, lists of delegates to scientific conferences, titles of technical publications, and even commercial documents scrolled swiftly down the high-resolution screen. A very efficient industrial espionage system had obviously been extremely busy; who would have thought that so many Japanese holomemory modules or Swiss gas-flow microcontrollers or German radiation detectors could have been traced to a destination in the dried lake bed of Lop Nor – the first milepost on their way to Jupiter?

Some of the items must have been included by accident; they could not possibly relate to the mission. If the Chinese had placed a secret order for one thousand infrared sensors through a dummy corporation in Singapore, that was only the concern of the military; it seemed highly unlikely that Tsien expected to be chased by heat-seeking missiles. And this one was really funny – specialized surveying and prospecting equipment from Glacier Geophysics, Inc., of Anchorage, Alaska. What lamebrain imagined that a deep-space expedition would have any need – the smile froze on Floyd's lips; he felt the skin crawl on the back of his neck. My God – they wouldn't dare! But they had already dared greatly; and now, at last, everything made sense.

He flashed back to the photos and conjectured plans of the Chinese ship. Yes, it was just conceivable – those flutings at the rear, alongside the drive deflection electrodes, would be about the right size.

Floyd called the bridge. 'Vasili.' he said, 'have you worked out their orbit yet?'

'Yes, I have,' the navigator replied, in a curiously subdued voice. Floyd could tell at once that something had turned up. He took a long shot.

'They're making a rendezvous with Europa, aren't they?'

There was an explosive gasp of disbelief from the other end.

'Chyort voz'mi! How did you know?'

'I didn't – I've just guessed it.'

'There can't be any mistake – I've checked the figures to six places. The braking manoeuvre worked out exactly as they intended. They're right on course for Europa – it couldn't have happened by chance. They'll be there in seventeen hours.'

'And go into orbit.'

'Perhaps; it wouldn't take much propellant. But what would be the point?'

'I'll risk another guess. They'll do a quick survey – and then they'll land.'

'You're crazy – or do you know something we don't?'

'No – it's just a matter of simple deduction. You're going to start kicking yourself for missing the obvious.'

'Okay, Sherlock, why should anyone want to land on Europa? What's there, for heaven's sake?'

Floyd was enjoying his little moment of triumph. Of course, he might still be completely wrong.

'What's on Europa? Only the most valuable substance in the Universe.'

He had overdone it; Vasili was no fool, and snatched the answer from his lips.

'Of course – water!'

'Exactly. Billions and billions of tons of it. Enough to fill up the propellant tanks – go cruising around all the satellites, and still have plenty left for the rendezvous with Discovery and the voyage home. I hate to say this, Vasili – but our Chinese friends have outsmarted us again.

'Always assuming, of course, that they can get away with it.'

Apart from the jet-black sky, the photo might have been taken almost anywhere in the polar regions of Earth; there was nothing in the least alien about the sea of wrinkled ice that stretched all the way out to the horizon. Only the five spacesuited figures in the foreground proclaimed that the panorama was of another world.

Even now, the secretive Chinese had not released the names of the crew. The anonymous intruders on the frozen Europan icescape were merely the chief scientist, the commander, the navigator, the first engineer, the second engineer. It was also ironic, Floyd could not help thinking, that everyone on Earth had seen the already historic photograph an hour before it reached Leonov, so much closer to the scene. But Tsien's transmissions were relayed on such a tight beam that it was impossible to intercept them; Leonov could receive only its beacon, broadcasting impartially in all directions. Even that was inaudible more than half the time, as Europa's rotation carried it out of sight, or the satellite itself was eclipsed by the monstrous bulk of Jupiter. All the scanty news of the Chinese mission had to be relayed from Earth.

The ship had touched down, after its initial survey, on one of the few islands of solid rock that protruded through the crust of ice covering virtually the entire moon. That ice was flat from pole to pole; there was no weather to carve it into strange shapes, no drifting snow to build up layer upon layer into slowly moving hills. Meteorites might fall upon airless Europa, but never a flake of snow. The only forces moulding its surface were the steady tug of gravity, reducing all elevations to one uniform level, and the incessant quakes caused by the other satellites as they passed and repassed Europa in their orbits. Jupiter itself, despite its far greater mass, had much less effect. The Jovian tides had finished their work aeons ago, ensuring that Europa remained locked forever with one face turned toward its giant master.