'There were mice in my bedroom last night,' Poole complained, only half seriously. 'Is there any chance you could find me a cat?'

Dr Wallace looked puzzled, then started to laugh.

'You must have heard one of the cleaning microts – I'll get the programming checked so they don't disturb you. Try not to step on one if you catch it at work; if you do, it will call for help, and all its friends will come to pick up the pieces.'

So much to learn – so little time! No, that wasn't true, Poole reminded himself. He might well have a century ahead of him, thanks to the medical science of this age. The thought was already beginning to fill him with apprehension rather than pleasure.

At least he was now able to follow most conversations easily, and had learned to pronounce words so that Indra was not the only person who could understand him. He was very glad that Anglish was now the world language, though French, Russian and Mandarin still flourished.

'I've another problem, Indra – and I guess you're the only person who can help. When I say "God", why do people look embarrassed?'

Indra did not look at all embarrassed; in fact, she laughed.

'That's a very complicated story. I wish my old friend Dr Khan was here to explain it to you – but he's on Ganymede, curing any remaining True Believers he can find there. When all the old religions were discredited – let me tell you about Pope Pius XX sometime – one of the greatest men in history! – we still needed a word for the Prime Cause, or the Creator of the Universe – if there is one...'

'There were lots of suggestions – Deo – Theo – Jove – Brahma – they were all tried, and some of them are still around – especially Einstein's favourite, "The Old One". But Deus seems to be the fashion nowadays.'

'I'll try to remember; but it still seems silly to me.'

'You'll get used to it: I'll teach you some other reasonably polite expletives, to use when you want to express your feelings...'

'You said that all the old religions have been discredited. So what do people believe nowadays?'

'As little as possible. We're all either Deists or Theists.'

'You've lost me. Definitions, please.'

'They were slightly different in your time, but here are the latest versions. Theists believe there's not more than one God; Deists that there is not less than one God.'

'I'm afraid the distinction's too subtle for me.'

'Not for everyone; you'd be amazed at the bitter controversies it's aroused. Five centuries ago, someone used what's known as surreal mathematics to prove there's an infinite number of grades between Theists and Deists. Of course, like most dabblers with infinity, he went insane. By the way, the best-known Deists were Americans – Washington, Franklin, Jefferson.'

'A little before my time – though you'd be surprised how many people don't realize it.'

'Now I've some good news. Joe – Prof. Anderson – has finally given his – what was the phrase? – OK. You're fit enough to go for a little trip upstairs... to the Lunar Level.'

'Wonderful. How far is that?'

'Oh, about twelve thousand kilometres.'

'Twelve thousand! That will take hours!'

Indra looked surprised at his remark: then she smiled.

'Not as long as you think. No – we don't have a Star Trek Transporter yet – though I believe they're still working on it! But you'll need new clothes, and someone to show you how to wear them. And to help you with the hundreds of little everyday jobs that can waste so much time. So we've taken the liberty of arranging a human personal assistant for you Come in, Danil.'

Danil was a small, light-brown man in his mid-thirties, who surprised Poole by not giving him the usual palm-top salute, with its automatic exchange of information.

Indeed, it soon appeared that Danil did not possess an Ident: whenever it was needed, he produced a small rectangle of plastic that apparently served the same purpose as the twenty-first century's 'smart cards'.

'Danil will also be your guide and what was that word? – I can never remember – rhymes with "ballet". He's been specially trained for the job. I'm sure you'll find him completely satisfactory.'

Though Poole appreciated this gesture, it made him feel a little uncomfortable. A valet, indeed! He could not recall ever meeting one; in his time, they were already a rare and endangered species. He began to feel like a character from an early-twentieth-century English novel.

'You have a choice,' said Indra, 'though I know which one you'll take. We can go up on an external elevator, and admire the view – or an interior one, and enjoy a meal and some light entertainment.'

'I can't imagine anyone wanting to stay inside.'

'You'd be surprised. It's too vertiginous for some people – especially visitors from down below. Even mountain climbers who say they've got a head for heights may start to turn green – when the heights are measured in thousands of kilometres, instead of metres.'

'I'll risk it,' Poole answered with a smile. 'I've been higher.'

When they had passed through a double set of airlocks in the exterior wall of the Tower (was it imagination, or did he feel a curious sense of disorientation then?) they entered what might have been the auditorium of a very small theatre. Rows of ten seats were banked up in five tiers: they all faced towards one of the huge picture windows which Poole still found disconcerting, as he could never quite forget the hundreds of tons of air pressure, striving to blast it out into space.

The dozen or so other passengers, who had probably never given the matter any thought, seemed perfectly at ease. They all smiled as they recognized him, nodded politely, then turned away to admire the view.

'Welcome to Skylounge,' said the inevitable autovoice. 'Ascent begins in five minutes. You will find refreshments and toilets on the lower floor.'

Just how long will this trip last? Poole wondered. We're going to travel over twenty thousand klicks, there and back: this will be like no elevator ride I've ever known on Earth...

While he was waiting for the ascent to begin, he enjoyed the stunning panorama laid out two thousand kilometres below. It was winter in the northern hemisphere, but the climate had indeed changed drastically, for there was little snow south of the Arctic Circle.

Europe was almost cloud-free, and there was so much detail that the eye was overwhelmed. One by one he identified the great cities whose names had echoed down the centuries; they had been shrinking even in his time, as the communications revolution changed the face of the world, and had now dwindled still further. There were also some bodies of water in improbable places – the northern Sahara's Lake Saladin was almost a small sea.

Poole was so engrossed by the view that he had forgotten the passage of time. Suddenly he realized that much more than five minutes had passed – yet the elevator was still stationary. Had something gone wrong – or were they waiting for late arrivals?

And then he noticed something so extraordinary that at first he refused to believe the evidence of his eyes. The panorama had expanded, as if he had already risen hundreds of kilometres! Even as he watched, he noticed new features of the planet below creeping into the frame of the window.

Then Poole laughed, as the obvious explanation occurred to him.

'You could have fooled me, Indra! I thought this was real – not a video projection!'

Indra looked back at him with a quizzical smile.

'Think again, Frank. We started to move about ten minutes ago. By now we must be climbing at, oh – at least a thousand kilometres an hour. Though I'm told these elevators can reach a hundred gee at maximum acceleration, we won't touch more than ten, on this short run.'