During the half-century since Tsien's disastrous landing, the ship had moved almost a thousand kilometres. It must have drifted – like Galaxy – for several years on the newly created Sea of Galilee, before coming to rest on its bleakly inhospitable shore.

Floyd picked up the radar echo as soon as Bill Tee flattened out at the end of its second leap across Europa. The signal was surprisingly weak for so large an object; as soon as they broke through the clouds, they realized why.

The wreck of the spaceship Tsien, first man-carrying vessel to land on a satellite of Jupiter, stood in the centre of a small, circular lake – obviously artificial, and connected by a canal to the sea, less than three kilometres away. Only the skeleton was left, and not even all of that; the carcass had been picked clean.

But by what? van der Berg asked. There was no sign of life there; the place looked as if it had been deserted for years. Yet he had not the slightest doubt that something had stripped the wreck, with deliberate and indeed almost surgical precision.

'Obviously safe to land,' said Floyd, waiting for a few seconds to get van der Berg's almost absentminded nod of approval. The geologist was already videoing everything in sight.

Bill Tee settled down effortlessly by the side of the pool, and they looked across the cold, dark water at this monument to man's exploring impulses. There seemed no convenient way of getting to the wreck, but that did not really matter.

When they had suited up, they carried the wreath to the water's edge, held it solemnly for a moment in front of the camera, then tossed in this tribute from Galaxy's crew. It had been beautifully made; even though the only raw materials available were metal foil, paper and plastic, one could easily believe that the flowers and leaves were real. Pinned all over them were notes and inscriptions, many written in the ancient but now officially obsolete script rather than Roman characters.

As they were walking back to the Bill Tee, Floyd said thoughtfully: 'Did you notice – there was practically no metal left. Only glass, plastic, synthetics.'

'What about those ribs and supporting girders?'

'Composite – mostly carbon, boron. Someone round here is very hungry for metal – and knows it when it sees it. Interesting...'

Very, thought van der Berg. On a world where fire could not exist, metals and alloys would be almost impossible to make, and as precious as – well, diamonds.

When he had reported to base, and received a message of gratitude from Second Officer Chang and his colleagues, Floyd took the Bill Tee up to a thousand metres and continued westward.

'Last lap,' he said, 'no point in going higher – we'll be there in ten minutes. But I won't land; if the Great Wall is what we think it is, I'd prefer not to. We'll do a quick flyby and head for home. Get those cameras ready; this could be even more important than Mount Zeus.'

And, he added to himself, I may soon know what Grandfather Heywood felt, not so far from here, fifty years ago. We'll have a lot to talk about when we meet – less than a week from now, if all goes well.

50 – Open City

What a terrible place, thought Chris Floyd – nothing but driving sleet, flurries of snow, occasional glimpses of landscapes streaked with ice – why, Haven was a tropical paradise by comparison! Yet he knew that the nightside, only a few hundred kilometres further on round the curve of Europa, was even worse.

To his surprise, the weather cleared suddenly and completely just before they reached their goal. The clouds lifted – and there ahead was an immense, black wall, almost a kilometre high, lying directly across Bill Tee's flight path. It was so huge that it was obviously creating its own microclimate; the prevailing winds were being deflected around it, leaving a local, calm area in its lee.

It was instantly recognizable as the Monolith, and sheltering at its foot were hundreds of hemispherical structures, gleaming a ghostly white in the rays of the low-hanging sun that had once been Jupiter. They looked, thought Floyd, exactly like old-style beehives made of snow; something in their appearance evoked other memories of Earth. Van der Berg was one jump ahead of him.

'Igloos,' he said. 'Same problem – same solution. No other building material around here, except rock – which would be much harder to work. And the low gravity must help – some of those domes are quite large. I wonder what lives in them...'

They were still too far away to see anything moving in the streets of this little city at the edge of the world. And as they came closer, they saw that there were no streets.

'It's Venice, made of ice,' said Floyd. 'All igloos and canals.'

'Amphibians,' answered van der Berg. 'We should have expected it. I wonder where they are?'

'We may have scared them. Bill Tee's much noisier outside than in.'

For a moment, van der Berg was too busy filming and reporting to Galaxy to reply. Then he said: 'We can't possibly leave without making some contact. You're right – this is far bigger than Mount Zeus.'

'And it could be more dangerous.'

'I don't see any sign of advanced technology – correction, that looks like an old twentieth-century radar dish over there! Can you get closer?'

'And get shot at? No thanks. Besides, we're using up our hover time. Only another ten minutes – if you want to get home again.'

'Can we at least land and look around? There's a patch of clear rock over there. Where the hell is everybody?'

'Scared, like me. Nine minutes. I'll do one trip across town – film everything you can – yes, Galaxy – we're OK – just rather busy at the moment – call you later -'

'I've just realized – that's not a radar dish, but something almost as interesting. It's pointing straight at Lucifer – it's a solar furnace! Makes a lot of sense in a place where the sun never moves – and you can't light a fire.'

'Eight minutes. Too bad everyone's hiding indoors.'

'Or back in the water. Can we look at that big building with the open space around it? I think it's the town hall.'

Van der Berg was pointing towards a structure much larger than all the others, and of quite different design; it was a collection of vertical cylinders, like oversized organ-pipes. Moreover, it was not the featureless white of the igloos, but showed a complex mottling over its entire surface.

'Europan art!' cried van der Berg. 'That's a mural of some kind! Closer, closer! We must get a record!'

Obediently, Floyd dropped lower – and lower – and lower. He seemed to have completely forgotten all his earlier reservations about hover time; and suddenly, with shocked incredulity, van der Berg realized that he was going to land.

The scientist tore his eyes from the rapidly approaching ground, and glanced at his pilot. Though he was obviously still in full control of Bill Tee, Floyd seemed to be hypnotized; he was staring at a fixed point straight ahead of the descending shuttle.

'What's the matter, Chris?' van der Berg cried. 'Do you know what you're doing?'

'Of course. Can't you see him?'

'See who?'

'That man, standing by the biggest cylinder. And he's not wearing any breathing gear!'

'Don't be an idiot, Chris: there's no one there.'

'He's looking up at us. He's waving – I think I recog – Oh my God!'

'There's no-one – no-one! Pull up!'

Floyd ignored him completely. He was absolutely calm and professional as he brought Bill Tee in to a perfect landing, and cut the motor at exactly the right instant before touchdown.

Very thoroughly, he checked the instrument readings, and set the safety switches. Only when he had completed the landing sequence did he again look out of the observation window, with a puzzled but happy expression on his face.