Dr van der Berg, who had started the whole thing – and had done very well out of it, professionally and financially – was now wondering what to do with his new opportunities. He had received many attractive offers from Earth universities and scientific organizations – but, ironically, it was impossible to take advantage of them. He had now lived too long at Ganymede's one-sixth of a gravity, and had passed the medical point of no return.

The Moon remained a possibility; so did Pasteur, as Heywood Floyd explained to him.

'We're trying to set up a space university there,' he said, 'so that off-worlders who can't tolerate one gee can still interact in real time with people on Earth. We'll have lecture halls, conference rooms, labs – some of them will only be computer-stored, but they'll look so real you'd never know. And you'll be able to go videoshopping on Earth, to make use of your ill-gotten gains.'

To his surprise, Floyd had not only rediscovered a grandson – he had adopted a nephew; he was now linked to van der Berg as well as Chris by a unique mix of shared experiences. Above all, there was the mystery of the apparition in the deserted Europan city, beneath the looming presence of the Monolith.

Chris had no doubts whatsoever. 'I saw you, and heard you, as clearly as I do now,' he told his grandfather. 'But your lips never moved – and the strange thing is that I didn't feel that was strange – it seemed perfectly natural. The whole experience had a – relaxed feeling about it. A little sad – no, wistful would be a better word. Or maybe resigned.'

'We couldn't help thinking of your encounter with Bowman, aboard Discovery,' added van der Berg.

'I tried to radio him before we landed on Europa. It seemed a naïve thing to do, but I couldn't imagine any alternative. I felt sure he was there, in some form or other.'

'And you never had any kind of acknowledgement?'

Floyd hesitated. The memory was fading fast, but he suddenly recalled that night when the mini-monolith had appeared in his cabin.

Nothing had happened, yet from that moment onwards he had felt that Chris was safe, and that they would meet again.

'No,' he said slowly. 'I never had any reply.' After all, it could only have been a dream.

VIII – THE KINGDOM OF SULPHUR

58 – Fire and Ice

Before the age of planetary exploration opened in the late twentieth century, few scientists would have believed that life could have flourished on a world so fan from the Sun. Yet for half a billion years, the hidden seas of Europa had been at least as prolific as those of Earth.

Before the ignition of Jupiter, a crust of ice had protected those oceans from the vacuum above. 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, which 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 this little world; the forces that convulsed Io were also working here, though with much less ferocity. The tug of war between planet and satellite caused continual submarine earthquakes, and avalanches which swept with amazing speed across the abyssal plains.

Scattered across those plains were countless oases, each extending for a few hundred metres around a cornucopia of mineral brines gushing from the interior. Depositing their chemicals in a tangled mass of pipes and chimneys, they sometimes created natural parodies of ruined castles or Gothic cathedrals, 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 seabed. Equally important, they brought from Europa's interior all the chemicals of life. Here, in an environment which would otherwise be totally hostile, were abundant energy and food. Such geothermal vents had been discovered in Earth's oceans, in the same decade that had given mankind its first glimpse of the Galilean satellites.

In the tropical zones close to the vents flourished myriads of delicate, spidery creatures that were the analogues of plants, though almost all were capable of movement. 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 source of heat – the submarine fire around which all these creatures warmed themselves – were sturdier, more robust organisms, not unlike crabs or spiders.

Armies of biologists could have spent lifetimes studying a single small oasis. Unlike the Palaeozoic terrestrial seas, Europa's hidden ocean was not a stable environment, so evolution had progressed swiftly here, producing multitudes of fantastic forms. And they were all under indefinite stay of execution; sooner or later, each fountain of life would weaken and die, as the forces that powered it moved their focus elsewhere. The abyss was littered with the evidence of such tragedies – cemeteries holding skeletons and mineral-encrusted remains where entire chapters had been deleted from the book of life.

There were huge shells, looking like trumpets larger than a man. There were clams of many shapes – bivalves, and even trivalves. And there were spiral stone patterns, many metres across, which seemed an exact analogy of the beautiful ammonites that disappeared so mysteriously from Earth's oceans at the end of the Cretaceous period.

In many places, fires burned in the abyss, as rivers of incandescent lava flowed for scores of kilometres along sunken valleys. The pressure at this depth was so great that the water in contact with the red-hot magma could not flash into steam, and the two liquids co-existed in an uneasy truce.

Here, on another world and with alien actors, something like the story of Egypt had been played long before the coming of man. As the Nile had brought life to a narrow ribbon of desert, so these rivers of warmth had vivified the Europan deep. Along their banks, in bands seldom more than a kilometre wide, species after species had evolved and flourished and passed away. And some had left monuments behind, in the shape of rocks piled on top of each other, or curious patterns of trenches engraved in the seabed.

Along the narrow bands of fertility in the deserts of the deep, whole cultures and primitive civilizations had risen and fallen. And the rest of their world had never known, for all these oases of warmth were as isolated from one another as the planets themselves. The creatures who basked in the glow of the lava river, and fed around the hot vents, could not cross the hostile wilderness between their lonely islands. If they had ever produced historians and philosophers, each culture would have been convinced that it was alone in the Universe.

And each was doomed. Not only were its energy sources sporadic and constantly shifting, but the tidal forces that drove them were steadily weakening. Even if they developed true intelligence, the Europans must perish with the final freezing of their world.

They were trapped between fire and ice – until Lucifer exploded in their sky, and opened up their universe.

And a vast rectangular shape, as black as night, materialized near the coast of a new-born continent.