Poole found it hard to avoid arousing suspicion, by the way he behaved towards his new crewmates as they prepared Falcon for what was supposed to be a short, routine flight. Only he and Chandler knew that it might be nothing of the kind.

Yet he was not heading into the totally unknown, as he and Dave Bowman had done a thousand years ago. Stored in the shuttle's memory were high-resolution maps of Europa showing details down to a few metres across. He knew exactly where he wished to go; it only remained to see if he would be allowed to break the centuries-long quarantine.

'Manual control, please.'

'Are you sure, Frank?'

'Quite sure, Falcon... Thank you.'

Illogical though it seemed, most of the human race had found it impossible not to be polite to its artificial children, however simple-minded they might be. Whole volumes of psychology, as well as popular guides (How Not to Hurt Your Computer's Feelings; Artificial Intelligence – Real irritation were two of the best-known titles) had been written on the subject of Man-Machine etiquette. Long ago it had been decided that, however inconsequential rudeness to robots might appear to be, it should be discouraged. All too easily, it could spread to human relationships as well.

Falcon was now in orbit, just as her flight-plan had promised, at a safe two thousand kilometres above Europa. The giant moon's crescent dominated the sky ahead, and even the area not illuminated by Lucifer was so brilliantly lit by the much more distant Sun that every detail was clearly visible. Poole needed no optical aid to see his planned destination, on the still-icy shore of the Sea of Galilee, not far from the skeleton of the first spacecraft to land on this world. Though the Europans had long ago removed all its metal components, the ill-fated Chinese ship still served as a memorial to its crew; and it was appropriate that the only 'town' – even if an alien one – on this whole world should have been named 'Tsienville'.

Poole had decided to come down over the Sea, and then fly very slowly towards Tsienville – hoping that this approach would appear friendly, or at least non-aggressive. Though he admitted to himself that this was very naïve, he could think of no better alternative.

Then, suddenly, just as he was dropping below the thousand-kilometre level, there was an interruption – not of the kind he had hoped for, but one which he had been expecting.

'This is Ganymede Control calling Falcon. You have departed from your flight-plan. Please advise immediately what is happening.'

It was hard to ignore such an urgent request, but in the circumstances it seemed the best thing to do.

Exactly thirty seconds later, and a hundred kilometres closer to Europa, Ganymede repeated its message. Once again Poole ignored it – but Falcon did not.

'Are you quite sure you want to do this, Frank?' asked the shuttle. Though Poole knew perfectly well that he was imagining it, he would have sworn there was a note of anxiety in its voice.

'Quite sure, Falcon. I know exactly what I'm doing.'

That was certainly untrue, and any moment now further lying might be necessary, to a more sophisticated audience.

Seldom-activated indicator lights started to flash near the edge of the control board. Poole smiled with satisfaction: everything was going according to plan.

'This is Ganymede Control! Do you receive me, Falcon? You are operating on manual override, so I am unable to assist you. What is happening? You are still descending towards Europa. Please acknowledge immediately.'

Poole began to experience mild twinges of conscience. He thought he recognized the Controller's voice, and was almost certain that it was a charming lady he had met at a reception given by the Mayor, soon after his arrival at Anubis. She sounded genuinely alarmed.

Suddenly, he knew how to relieve her anxiety – as well as to attempt something which he had previously dismissed as altogether too absurd. Perhaps, after all, it was worth a try: it certainly wouldn't do any harm – and it might even work.

'This is Frank Poole, calling from Falcon. I am perfectly OK – but something seems to have taken over the controls, and is bringing the shuttle down towards Europa. I hope you are receiving this – I will continue to report as long as possible.'

Well, he hadn't actually lied to the worried Controller, and one day he hoped he would be able to face her with a clear conscience.

He continued to talk, trying to sound as if he was completely sincere, instead of skirting the edge of truth.

'This is Frank Poole aboard the shuttle Falcon, descending towards Europa. I assume that some outside force has taken charge of my spacecraft, and will be landing it safely.'

'Dave – this is your old shipmate Frank. Are you the entity that is controlling me? I have reason to think that you are on Europa.

'If so – I look forward to meeting you – wherever or whatever you are.'

Not for a moment did he imagine there would be any reply: even Ganymede Control appeared to be shocked into silence.

And yet, in a way, he had an answer. Falcon was still being permitted to descend towards the Sea of Galilee.

Europa was only fifty kilometres below; with his naked eyes Poole could now see the narrow black bar where the greatest of the Monoliths stood guard – if indeed it was doing that – on the outskirts of Tsienville.

No human being had been allowed to come so close for a thousand years.

For millions of years it had been an ocean world, its hidden waters protected from the vacuum of space by a crust of ice. In most places the ice was kilometres thick, but there were lines of weakness where it had cracked open and torn apart. Then there had been a brief battle between two implacably hostile elements that came into direct contact on no other world in the Solar System, The war between Sea and Space always ended in the same stalemate; the exposed water simultaneously boiled and froze, repairing the armour of ice.

The seas of Europa would have frozen completely solid long ago without the influence of nearby Jupiter. Its gravity continually kneaded the core of the little world; the forces that convulsed Io were also working there, though with much less ferocity. Everywhere in the deep was evidence of that tug-of-war between planet and satellite, in the continual roar and thunder of submarine earthquakes, the shriek of gases escaping from the interior, the infrasonic pressure waves of avalanches sweeping over the abyssal plains. By comparison with the tumultuous ocean that covered Europa, even the noisy seas of Earth were muted.

Here and there, scattered over the deserts of the deep, were oases that would have amazed and delighted any terrestrial biologist. They extended for several kilometres around tangled masses of pipes and chimneys deposited by mineral brines gushing from the interior. Often they created natural parodies of Gothic castles, from which black, scalding liquids pulsed in a slow rhythm, as if driven by the beating of some mighty heart. And like blood, they were the authentic sign of life itself.

The boiling fluids drove back the deadly cold leaking down from above, and formed islands of warmth on the sea-bed. Equally important, they brought from Europa's interior all the chemicals of life. Such fertile oases, offering food and energy in abundance, had been discovered by the twentieth-century explorers of Earth's oceans. Here they were present on an immensely larger scale, and in far greater variety.

Delicate, spidery structures that seemed to be the analogue of plants flourished in the 'tropical' zones closest to the sources of heat. Crawling among these were bizarre slugs and worms, some feeding on the plants, others obtaining their food directly from the mineral-laden waters around them. At greater distances from the submarine fires around which all these creatures warmed themselves lived sturdier, more robust organisms, not unlike crabs or spiders.