Perhaps that was good news for men. Even if they were encumbered with spacesuits, there was probably nothing on Europa that could catch them -even if it wanted to.

Captain Laplace found wry amusement in handing over the operation of his ship to the purser; he wondered if this situation was unique, in the annals of space and sea.

Not that there was a great deal that Mr Lee could do. Galaxy was floating vertically, one-third out of the water, heeling slightly before a wind that was driving it at a steady five knots. There were only a few leaks below the waterline, easily handled. Equally important, the hull was still airtight.

Although most of the navigation equipment was useless, they knew exactly where they were. Ganymede gave them an accurate fix on their emergency beacon every hour, and if Galaxy kept to her present course she would make landfall on a large island within the next three days. If she missed that, she would head on out to the open sea, and eventually reach the tepidly boiling zone immediately underneath Lucifer. Though not necessarily catastrophic, that was a most unattractive prospect; Acting Captain Lee spent much of his time thinking of ways to avoid it.

Sails – even if he had suitable material and rigging – would make very little difference to their course. He had lowered improvised sea-anchors down to five hundred metres, looking for currents that might be useful, and finding none. Nor had he found the bottom; it lay unknown kilometres further down.

Perhaps that was just as well; it protected them from the submarine quakes that continually. racked this new ocean. Sometimes Galaxy would shake as if struck by a giant hammer, as a shockwave went racing by. In a few hours, a tsunami, dozens of metres high, would crash upon some Europan shore; but here in deep water the deadly waves were little more than ripples.

Several times, sudden vortexes were observed at a distance; they looked quite dangerous – maelstroms that might even suck Galaxy down to unknown depths – but luckily they were too far off to do more than make the ship spin around a few times in the water.

And just once, a huge bubble of gas rose and burst only a hundred metres away. It was most impressive, and everyone seconded the doctor's heartfelt comment: 'Thank God we can't smell it.'

It is surprising how quickly the most bizarre situation can become routine. Within a few days, life aboard Galaxy had settled down to a steady routine, and Captain Laplace's main problem was keeping the crew occupied. There was nothing worse for morale than idleness, and he wondered how the skippers of the old windjammers had kept their men busy on those interminable voyages. They couldn't have spent all their time scrambling up the rigging or cleaning the decks.

He had the opposite problem with the scientists. They were always proposing tests and experiments, which had to be carefully considered before they could be approved. And if he allowed it, they would have monopolized the ship's now very limited communications channels.

The main antenna complex was now being battered around at the waterline, and Galaxy could no longer talk directly to Earth. Everything had to be relayed through Ganymede, on a bandwidth of a few miserable megahertz. A single live video channel pre-empted everything else, and he had to resist the clamour of the terrestrial networks. Not that they would have a great deal to show their audiences, except open sea, cramped ship interiors, and a crew which, though in good spirits, was becoming steadily more hirsute.

An unusual amount of traffic seemed directed to Second Officer Floyd whose encrypted responses were so brief that they could not have contained much information. Laplace finally decided to have a talk to the young man.

'Mr Floyd,' he said, in the privacy of his cabin. 'I'd appreciate it if you would enlighten me about your part-time occupation.'

Floyd looked embarrassed, and clutched at the table as the ship rocked slightly in a sudden gust.

'I wish I could, sir, but I'm not permitted.'

'By whom, may I ask?'

'Frankly, I'm not sure.'

That was perfectly true. He suspected it was ASTROPOL, but the two quietly impressive gentlemen who had briefed him on Ganymede had unaccountably failed to provide this information.

'As captain of this ship – especially in the present circumstances – I would like to know what's going on here. If we get out of this, I'm going to spend the next few years of my life at Courts of Enquiry. And you'll probably be doing the same.'

Floyd managed a wry grin.

'Hardly worth being rescued, is it, Sir? All I know is that some high-level agency expected trouble on this mission, but didn't know what form it would take. I was just told to keep my eyes open. I'm afraid I didn't do much good, but I imagine I was the only qualified person they could get hold of in time.'

'I don't think you can blame yourself. Who would have imagined that Rosie -'

The Captain paused, struck by a sudden thought.

'Do you suspect anyone else?' He felt like adding 'Me, for instance?', but the situation was already sufficiently paranoiac.

Floyd looked thoughtful, then apparently came to a decision.

'Perhaps I should have spoken to you before, Sir, but I know how busy you've been. I'm sure Dr van der Berg is involved somehow. He's a Mede, of course; they're odd people, and I don't really understand them.' Or like them, he might have added. Too clannish – not really friendly to offworlders. Still, one could hardly blame them; all pioneers trying to tame a new wilderness were probably much the same.

'Van der Berg – hmm. What about the other scientists?'

'They've been checked, of course. All perfectly legitimate, and nothing unusual about any of them.'

That was not altogether true. Dr Simpson had more wives than was strictly legal, at least at one time, and Dr Higgins had a large collection of most curious books. Second Officer Floyd was not quite sure why he had been told all this; perhaps his mentors merely wanted to impress him with their omniscience. He decided that working for ASTROPOL (or whoever it was) had some entertaining fringe benefits.

'Very well,' said the Captain, dismissing the amateur agent. 'But please keep me informed if you discover anything – anything at all– that might affect the safety of the ship.'

In the present circumstances, it was hard to imagine what that might be. Any further hazards seemed slightly superfluous.

Even twenty-four hours before they sighted the island, it was still not certain whether Galaxy would miss it and be blown on out into the emptiness of the central ocean. Her position, as observed by the Ganymede radar, was plotted on a large chart which everyone aboard examined anxiously several times a day.

Even if the ship did reach land, her problems might be just beginning. She might be pounded to pieces on a rocky coast, rather than gently deposited on some conveniently shelving beach.

Acting Captain Lee was keenly aware of all these possibilities. He had once been shipwrecked himself, in a cabin cruiser whose engines had failed at a critical moment, off the island of Bali. There had been little danger, though a good deal of drama, and he had no wish to repeat the experience – especially as there was no coastguard here to come to the rescue.

There was a truly cosmic irony in their plight. Here they were, aboard one of the most advanced transportation devices ever made by man – capable of crossing the Solar System! – yet now they could not deflect it more than a few metres from its course. Nevertheless, they were not completely helpless; Lee still had a few cards to play.

On this sharply curving world, the island was only five kilometres away when they first sighted it. To Lee's great relief, there were none of the cliffs he had feared; nor, on the other hand, was there any sign of the beach he had hoped for. The geologists had warned him that he was a few million years too early to find sand here; the mills of Europa, grinding slowly, had not yet had time to do their work.