And they were all made from the same material, which gleamed a ghostly white in the double daylight. On Earth, the Esquimaux had found the identical answer to the challenge of their own frigid, materials-poor environment; Tsienville's igloos were also made of ice.

In lieu of streets, there were canals – as best suited creatures who were still amphibious, and apparently returned to the water to sleep. Also, it was believed, to feed and to mate, though neither hypothesis had been proved.

Tsienville had been called 'Venice, made of ice', and Poole had to agree that it was an apt description. However, there were no Venetians in sight; the place looked as if it had been deserted for years.

And here was another mystery; despite the fact that Lucifer was fifty times brighter than the distant Sun, and was a permanent fixture in the sky, the Europs still seemed locked to an ancient rhythm of night and day. They returned to the ocean at sunset, and emerged with the rising of the Sun – despite the fact that the level of illumination had changed by only a few per cent. Perhaps there was a parallel on Earth, where the life cycles of many creatures were controlled as much by the feeble Moon as the far more brilliant Sun.

It would be sunrise in another hour, and then the inhabitants of Tsienville would return to land and go about their leisurely affairs – as by human standards, they certainly were. The sulphur-based biochemistry that powered the Europs was not as efficient as the oxygen-driven one that energized the vast majority of terrestrial animals. Even a sloth could outrun a Europ, so it was difficult to regard them as potentially dangerous. That was the Good News; the Bad News was that even with the best intentions on both sides, attempts at communication would be extremely slow – perhaps intolerably tedious.

It was about time, Poole decided, that he reported back to Ganymede Control. They must be getting very anxious, and he wondered how his co-conspirator, Captain Chandler, was dealing with the situation.

'Falcon calling Ganymede. As you can doubtless see, I have – er – been brought to rest just above Tsienville. There is no sign of hostility, and as it's still solar night here all the Europs are underwater. Will call you again as soon as I'm on the ground.'

Dim would have been proud of him, Poole thought, as he brought Falcon down gently as a snowflake on a smooth patch of ice. He was taking no chances with its stability, and set the inertial drive to cancel all but a fraction of the shuttle's weight – just enough, he hoped, to prevent it being blown away by any wind.

He was on Europa – the first human in a thousand years. Had Armstrong and Aldrin felt this sense of elation, when Eagle touched down on the Moon? Probably they were too busy checking their Lunar Module's primitive and totally unintelligent systems. Falcon, of course, was doing all this automatically. The little cabin was now very quiet, apart from the inevitable – and reassuring – murmur of well-tempered electronics. It gave Poole a considerable shock when Chandler's voice, obviously pre-recorded, interrupted his thoughts.

'So you made it! Congratulations! As you know, we're scheduled to return to the Belt week after next, but that should give you plenty of time.'

'After five days, Falcon knows what to do. She'll find her way home, with or without you. So good luck!'

MISS PRINGLE

ACTIVATE CRYPTO PROGRAM

STORE

Hello, Dim – thanks for that cheerful message! I feel rather silly using this program – as if I'm a secret agent in one of the spy melodramas that used to be so popular before I was born. Still, it will allow some privacy, which may be useful. Hope Miss Pringle has downloaded it properly... of course, Miss P, I'm only joking!

By the way, I'm getting a barrage of requests from all the news media in the Solar System. Please try to hold them off – or divert them to Dr Ted. He'll enjoy handling them...

Since Ganymede has me on camera all the time, I won't waste breath telling you what I'm seeing. If all goes well, we should have some action in a few minutes – and we'll know if it really was a good idea to let the Europs find me already sitting here peacefully, waiting to greet them when they come to the surface...

Whatever happens, it won't be as big a surprise to me as it was to Dr Chang and his colleagues, when they landed here a thousand years ago! I played his famous last message again, just before leaving Ganymede. I must confess it gave me an eerie feeling – couldn't help wondering if something like that could possibly happen again... wouldn't like to immortalize myself the way poor Chang did...

Of course, I can always lift off if something starts going wrong... and here's an interesting thought that's just occurred to me... I wonder if the Europs have any history – any kind of records... any memory of what happened just a few kilometres from here, a thousand years ago?

...This is Dr Chang, calling from Europa. I hope you cart hear me, especially Dr Floyd – I know you're aboard Leonov... I may not have much time... aiming my suit antenna where I think you are... please relay this information to Earth.

Tsien was destroyed three hours ago. I'm the only survivor. Using my suit radio – no idea if it has enough range, but it's the only chance. Please listen carefully...

THERE IS LIFE ON EUROPA. I repeat: THERE IS LIFE ON EUROPA...

We landed safely, checked all the systems, and ran out the hoses so we could start pumping water into our propellant tanks immediately... just in case we had to leave in a hurry.

Everything was going according to plan... it seemed almost too good to be true. The tanks were half full when Dr Lee and I went out to check the pipe insulation. Tsien stands – stood – about thirty metres from the edge of the Grand Canal. Pipes went directly from it and down through the ice. Very thin – not safe to walk on.

Jupiter was quarter full, and we had five kilowatts of lighting strung up on the ship. She looked like a Christmas tree – beautiful, reflected on the ice...

Lee saw it first – a huge dark mass rising up from the depths. At first we thought it was a school of fish – too large for a single organism – then it started to break through the ice, and began moving towards us.

It looked rather like huge strands of wet seaweed, crawling along the ground. Lee ran back to the ship to get a camera – I stayed to watch, reporting over the radio. The thing moved so slowly I could easily outrun it. I was much more excited than alarmed. Thought I knew what kind of creature it was – I've seen pictures of the kelp forests off California – but I was quite wrong.

I could tell it was in trouble. It couldn't possibly survive at a temperature a hundred and fifty below its normal environment. It was freezing solid as it moved forward -bits were breaking off like glass – but it was still advancing towards the ship, a black tidal wave, slowing down all the time.

I was still so surprised that I couldn't think straight and I couldn't imagine what it was trying to do. Even though it was heading towards Tsien it still seemed completely harmless, like – well, a small forest on the move. I remember smiling – it reminded me of Macbeth's Birnam Wood...

Then I suddenly realized the danger. Even if it was completely inoffensive – it was heavy – with all the ice it was carrying, it must have weighed several tons, even in this low gravity.

And it was slowly, painfully climbing up our landing gear... the legs were beginning to buckle, all in slow motion, like something in a dream – or a nightmare...

Not until the ship started to topple did I realize what the thing was trying to do – and then it was far too late. We could have saved ourselves – if we'd only switched off our lights!