'Communications?'

'The line's got fibre optics in it. And his suit radio will probably work most of the way.'

'Umm. Where does he want to go in?'

'The best place is that extinct geyser at the base of Etna Junior. It's been dead for at least a thousand years.'

'So I suppose it should keep quiet for another couple of days. Very well – does anyone else want to go?'

'Cliff Greenburg has volunteered – he's done a good deal of underwater cave-exploring, in the Bahamas.'

'I tried it once – that was enough. Tell Cliff he's much too valuable. He can go in as far as he can still see the entrance – and no further. And if he loses contact with Chant, he's not to go after him, without my authority.'

Which, the Captain added to himself, I would be very reluctant to give...

Dr Chant knew all the old jokes about speleologists wanting to return to the womb, and was quite sure he could refute them.

'That must be a damn noisy place, with all its thumpings and bumpings and gurglings,' he argued. 'I love caves because they're so peaceful and timeless. You know that nothing has changed for a hundred thousand years, except that the stalactites have grown a bit thicker.'

But now, as he drifted deeper into Halley, playing out the thin, but virtually unbreakable thread that linked him to Clifford Greenburg, he realized that this was no longer true. As yet, he had no scientific proof, but his geologist's instincts told him that this subterranean world had been born only yesterday, on the time-scale of the Universe. It was younger than some of the cities of man.

The tunnel through which he was gliding in long, shallow leaps was about four metres in diameter, and his virtual weightlessness brought back vivid memories of cave-diving on Earth. The low gravity contributed to the illusion; it was exactly as if he was carrying slightly too much weight, and so kept drifting gently downwards. Only the absence of all resistance reminded him that he was moving through vacuum, not water.

'You're just getting out of sight,' said Greenburg, fifty metres in from the entrance. 'Radio link still fine. What's the scenery like?'

'Very hard to say – I can't identify any formations, so I don't have the vocabulary to describe them. It's not any kind of rock – it crumbles when I touch it – I feel as if I'm exploring a giant Gruyère cheese.'

'You mean it's organic?'

'Yes – nothing to do with life, of course – but perfect raw material for it. All sorts of hydrocarbons – the chemists will have fun with these samples. Can you still see me?'

'Only the glow of your light, and that's fading fast.'

'Ah – here's some genuine rock – doesn't look as if it belongs here – probably an intrusion – ah – I've struck gold!'

'You're joking!'

'It fooled a lot of people in the old West – iron pyrites. Common on the outer satellites, of course, but don't ask me what it's doing here...'

'Visual contact lost. You're two hundred metres in.'

'I'm passing through a distinct layer – looks like meteoric debris – something exciting must have happened back then – I hope we can date it – wow!'

'Don't do that sort of thing to me!'

'Sorry – quite took my breath away – there's a big chamber ahead – last thing I expected – let me swing the beam around...

'Almost spherical – thirty, forty metres across. And – I don't believe it – Halley is full of surprises – stalactites, stalagmites.'

'What's so surprising about that?'

'No free water, no limestone here, of course – and such low gravity. Looks like some kind of wax. Just a minute while I get good video coverage... fantastic shapes... sort of thing a dripping candle makes... that's odd...'

'Now what?'

Dr Chant's voice had shown a sudden alteration in tone, which Greenburg had instantly detected.

'Some of the columns have been broken. They're lying on the floor. It's almost as if...'

'Go on!'

'... as if something has – blundered – into them.'

'That's crazy. Could an earthquake have snapped them?'

'No earthquakes here – only microseisms from the geysers. Perhaps there was a big blow-out at some time. Anyway, it was centuries ago. There's a film of this wax stuff over the fallen columns – several millimetres thick.'

Dr Chant was slowly recovering his composure. He was not a highly imaginative man – spelunking eliminates such men rather quickly – but the very feel of the place had triggered some disturbing memory. And those fallen columns looked altogether too much like the bars of a cage, broken by some monster in an attempt to escape.

Of course, that was perfectly absurd – but Dr Chant had learned never to ignore any premonition, any danger signal, until he had traced it to its origin. That caution had saved his life more than once; he would not go beyond this chamber until he had identified the source of his fear. And he was honest enough to admit that 'fear' was the correct word.

'Bill – are you all right? What's happening?'

'Still filming. Some of these shapes remind me of Indian temple sculpture. Almost erotic.'

He was deliberately turning his mind away from the direct confrontation of his fears, hoping thereby to sneak up on them unawares, by a kind of averted mental vision. Meanwhile the purely mechanical acts of recording and collecting samples occupied most of his attention.

There was nothing wrong, he reminded himself, with healthy fear; only when it escalated into panic did it become a killer. He had known panic twice in his life (once on a mountainside, once underwater) and still shuddered at the memory of its clammy touch. Yet – thankfully – he was far from it now, and for a reason which, though he did not understand it, he found curiously reassuring. There was an element of comedy in the situation.

And presently he started to laugh – not with hysteria, but with relief.

'Did you ever see those old Star Wars movies?' he asked Greenburg.

'Of course – half a dozen times.'

'Well, I know what's been bothering me. There was a sequence when Luke's spaceship dives into an asteroid – and runs into a gigantic snake-creature that lurks inside its caverns.'

'Not Luke's ship – Hans Solo's Millennium Falcon. And I always wondered how that poor beast managed to eke out a living. It must have grown very hungry, waiting for the occasional titbit from space. And Princess Leia wouldn't have been more than an hors-d'oeuvre, anyway.'

'Which I certainly don't intend to provide,' said Dr Chant, now completely at ease. 'Even if there is life here – which would be marvellous – the food chain would be very short. So I'd be surprised to find anything bigger than a mouse. Or, more likely, a mushroom... Now let's see – where do we go from here... There are two exits on the other side of the chamber... the one on the right is bigger... I'll take that...'

'How much more line have you got?'

'Oh, a good half-kilometre. Here we go... I'm in the middle of the chamber... damn, bounced off the wall... now I've got a hand-hold... going in head-first... smooth walls, real rock for a change... that's a pity..

'What's the problem?'

'Can't go any further. More stalactites... too close together for me to get through... and too thick to break without explosives. And that would be a shame... the colours are beautiful... first real greens and blues I've seen on Halley. Just a minute while I get them on video...

Dr Chant braced himself against the wall of the narrow tunnel, and aimed the camera. With his gloved fingers be reached for the HI-INTENSITY switch, but missed it and cut off the main lights completely.

'Lousy design,' he muttered. 'Third time I've done that.'

He did not immediately correct his mistake, because he had always enjoyed that silence and total darkness which can be experienced only in the deepest caves. The gentle background noises of his life-support equipment robbed him of the silence, but at least...