'Maybe you're wondering how I get on with Captain Tanya. Well, I like her very much – but I'd hate to make her angry. There's no doubt exactly who runs this ship.

'And Surgeon-Commander Rudenko – you met her at the Honolulu Aerospace Convention two years ago, and I'm sure you won't have forgotten that last party. You'll understand why we all call her Catherine the Great – behind her broad back, of course.

'But that's enough gossip. If I run overtime, I hate to think of the surcharge. And by the way, these personal calls are supposed to be completely private. But there are a lot of links in the communications chain, so don't be surprised if you occasionally get messages by – well, another route.

'I'll be waiting to hear from you – tell the girls I'll be speaking to them later. My love to you all – I miss you and Chris very badly. And when I get back, I promise I'll never leave again.'

There was a brief hissing pause, then an obviously synthetic voice said: 'This terminates Transmission Four Hundred Thirty-two Stroke Seven from Spacecraft Leonov.' As Caroline Floyd switched off the speaker, the two dolphins slid beneath the surface of the pool and glided out into the Pacific, leaving scarcely a ripple in the water.

When he realized that his friends were gone, Christopher began to cry. His mother picked him up in her arms and tried to comfort him, but it was a long time before she succeeded.

The image of Jupiter, with its ribbons of white cloud, its mottled bands of salmon pink, and the Great Red Spot staring out like a baleful eye, hung steady on the flight-deck projection screen. It was three-quarters full, but no one was looking at the illuminated disk; all eyes were focused on the crescent of darkness at its edge. There, over the nightside of the planet, the Chinese ship was about to meet its moment of truth.

This is absurd, thought Floyd. We can't possibly see anything across forty million kilometres. And it doesn't matter; the radio will tell us all we want to know.

Tsien had closed down all voice, video, and data circuits two hours before, as the long-range antennas were withdrawn into the protective shadow of the heat shield. Only the omnidirectional beacon was still transmitting, accurately pinpointing the Chinese ship's position as it plunged toward that ocean of continent-sized clouds. The shrill beep... beep... beep... was the only sound in Leonov's control room. Each of those pulses had left Jupiter more than two minutes earlier; by this time, their source might already be a cloud of incandescent gas, dispersing in the Jovian stratosphere.

The signal was fading, becoming noisy. The beeps were getting distorted; several dropped out completely, then the sequence returned. A plasma sheath was building up around Tsien and soon would cut off all communications until the ship re-emerged. If it ever did.

'Posmotri!' cried Max. 'There it is!'

At first Floyd could see nothing. Then, just off the edge of the illuminated disk, he made out a tiny star – gleaming where no star could possibly be, against the darkened face of Jupiter.

It appeared quite motionless, though he knew it must be moving at a hundred kilometres a second. Slowly it grew in brilliance; and then it was no longer a dimensionless point, but was becoming elongated. A man-made comet was streaking across the Jovian night sky, leaving a trail of incandescence thousands of kilometres in length.

One last badly distorted and curiously drawn-out beep sounded from the tracking beacon, then only the meaningless hiss of Jupiter's own radiation, one of those many cosmic voices that had nothing to do with Man or his works.

Tsien was inaudible, but not yet invisible. For they could see that the tiny elongated spark had indeed moved appreciably away from the sunward face of the planet and would soon disappear into the nightside. By then, if all had gone according to plan, Jupiter would have captured the ship, destroying its unwanted velocity. When it emerged from behind the giant world, it would be another Jovian satellite.

The spark flickered out. Tsien had rounded the curve of the planet and was heading over the nightside. There would be nothing to see, or to hear, until it emerged from shadow – if all went well, in just under an hour. It would be a very long hour for the Chinese.

To Chief Scientist Vasili Orlov and communications engineer Sasha Kovalev, the hour went extremely quickly. There was much they could learn from observations of that little star; its times of appearance and disappearance and, above all, the Doppler shift of the radio beacon gave vital information about Tsien's new orbit. Leonov's computers were already digesting the figures, and spitting out projected times of re-emergence based on various assumptions about rates of deceleration in the Jovian atmosphere.

Vasili switched off the computer display, spun around in his chair, loosened his seat belt, and addressed the patiently waiting audience.

'Earliest reappearance is in forty-two minutes. Why don't you spectators go for a walk, so we can concentrate on getting all this into good shape? See you in thirty-five minutes. Shoo! Nu ukhodi!'

Reluctantly, the unwanted bodies left the bridge – but, to Vasili's disgust, everyone was back again in little more than thirty minutes. He was still chiding them for their lack of faith in his calculations when the familiar beep... beep... beep... of Tsien's tracking beacon burst from the loudspeakers.

Vasili looked astonished and mortified, but soon joined in the spontaneous round of applause; Floyd could not see who first started the clapping. Rivals though they might be, they were all astronauts together, as far from home as any men had ever travelled – 'Ambassadors for Mankind', in the noble words of the first UN Space Treaty. Even if they did not want the Chinese to succeed, neither did they wish them to meet disaster.

A large element of self-interest was also involved, Floyd could not help thinking. Now the odds in Leonov's own favour were significantly improved; Tsien had demonstrated that the aerobraking manoeuvre was indeed possible. The data on Jupiter was correct; its atmosphere did not contain unexpected and perhaps fatal surprises.

'Well!' said Tanya. 'I suppose we should send them a message of congratulations. But even if we did, they wouldn't acknowledge it.'

Some of his colleagues were still making fun of Vasili, who was staring at his computer output in frank disbelief.

'I don't understand it!' he exclaimed. 'They should still be behind Jupiter! Sasha – give me a velocity reading on their beacon!'

Another silent dialogue was held with the computer; then Vasili gave a long, low whistle.

'Something's wrong. They're in a capture orbit, all right – but it won't let them make a rendezvous with Discovery. The orbit they're on now will take them way beyond Io – I'll have more accurate data when we've tracked them for another five minutes.'

'Anyway, they must be in a safe orbit,' said Tanya. 'They can always make corrections later.'

'Perhaps. But that could cost them days, even if they have the fuel. Which I doubt.'

'So we may still beat them.'

'Don't be such an optimist. We're still three weeks from Jupiter. They can make a dozen orbits before we get there, and choose the most favourable one for a rendezvous.'

'Again – assuming that they have enough propellant.'

'Of course. And that's something we can only make educated guesses about.'

All this conversation took place in such rapid and excited Russian that Floyd was left far behind. When Tanya took pity on him and explained that Tsien had overshot and was heading for the outer satellites, his first reaction was: 'Then they may be in serious trouble. What will you do if they appeal for help?'