None of the other children at the Station could help. They were immersed in their games in Playroom, or chewing pencils over their tests and homework.

‘Abel, what’s the matter?’ Zenna Peters called after him as he wandered off to the empty store-room on D-Deck. ‘You’re looking sad again.’

Abel hesitated, watching Zenna’s warm, puzzled smile, then slipped his hands into his pockets and made off, springing down the metal stairway to make sure she didn’t follow him. Once she sneaked into the store-room uninvited and he had pulled the light-bulb out of the socket, shattered about three weeks of conditioning. Dr Francis had been furious.

As he hurried along the D-Deck corridor he listened carefully for the doctor, who had recently been keeping an eye on Abel, watching him shrewdly from behind the plastic models in Playroom. Perhaps Abel’s mother had told him about the nightmare, when he would wake from a vice of sweating terror, an image of a dull burning disc fixed before his eyes.

If only Dr Francis could cure him of that dream.

Every six yards down the corridor he stepped through a bulkhead, and idly touched the heavy control boxes on either side of the doorway. Deliberately unfocusing his mind, Abel identified some of the letters above the switches M-T-R SC-N but they scrambled into a blur as soon as he tried to read the entire phrase. Conditioning was too strong. After he trapped her in the store-room Zenna had been able to read a few of the notices, but Dr Francis whisked 321 her away before she could repeat them. Hours later, when she came back, she remembered nothing.

As usual when he entered the store-room, he waited a few seconds before switching on the light, seeing in front of him the small disc of burning light that in his dreams expanded until it filled his brain like a thousand arc lights. It seemed endlessly distant, yet somehow mysteriously potent and magnetic, arousing dormant areas of his mind close to those which responded to his mother’s presence.

As the disc began to expand he pressed the switch tab.

To his surprise, the room remained in darkness. He fumbled for the switch, a short cry slipping involuntarily through his lips.

Abruptly, the light went on.

‘Hello, Abel,’ Dr Francis said easily, right hand pressing the bulb into its socket. ‘Quite a shock, that one.’ He leaned against a metal crate. ‘I thought we’d have a talk together about your essay.’ He took an exercise book out of his white plastic suit as Abel sat down stiffly. Despite his dry smile and warm eyes there was something about Dr Francis that always put Abel on his guard.

Perhaps Dr Francis knew too?

‘The Closed Community,’ Dr Francis read out. ‘A strange subject for an essay, Abel.’

Abel shrugged. ‘It was a free choice. Aren’t we really expected to choose something unusual?’

Dr Francis grinned. ‘A good answer. But seriously, Abel, why pick a subject like that?’

Abel fingered the seals on his suit. These served no useful purpose, but by blowing through them it was possible to inflate the suit. ‘Well, it’s a sort of study of life at the Station, how we all get on with each other. What else is there to write about? I don’t see that it’s so strange.’

‘Perhaps not. No reason why you shouldn’t write about the Station. All four of the others did too. But you called yours "The Closed Community". The Station isn’t closed, Abel, is it?’

‘It’s closed in the sense that we can’t go outside,’ Abel explained slowly. ‘That’s all I meant.’

‘Outside,’ Dr Francis repeated. ‘It’s an interesting concept. You must have given the whole subject a lot of thought. When did you first start thinking along these lines?’

‘After the dream,’ Abel said. Dr Francis had deliberately sidestepped his use of the word ‘outside’ and he searched for some means of getting to the point. In his pocket he felt the small plumbline he carried around. ‘Dr Francis, perhaps you can explain something to me. Why is the Station revolving?’

‘Is it?’ Dr Francis looked up with interest. ‘How do you know?’

Abel reached up and fastened the plumbline to the ceiling stanchion.

‘The interval between the ball and the wall is about an eighth of an inch greater at the bottom than at the top. Centrifugal forces are driving it outwards. I calculated that the Station is revolving at about two feet per second.’

Dr Francis nodded thoughtfully. ‘That’s just about right,’ he said matter-of-factly. He stood up. ‘Let’s take a trip to my office. It looks as if it’s time you and I had a serious talk.’

The Station was on four levels. The lower two contained the crew’s quarters, two circular decks of cabins which housed the 14 people on board the Station. The senior clan was the Peters, led by Captain Theodore, a big stern man of taciturn disposition who rarely strayed from Control. Abel had never been allowed there, but the Captain’s son, Matthew, often described the hushed dome-like cabin filled with luminous dials and flickering lights, the strange humming music.

All the male members of the Peters clan worked in Control — grandfather Peters, a white-haired old man with humorous eyes, had been Captain before Abel was born — and with the Captain’s wife and Zenna they constituted the elite of the Station.

However, the Grangers, the clan to which Abel belonged, was in many respects more important, as he had begun to realize. The day-to-day running of the Station, the detailed programming of emergency drills, duty rosters and commissary menus, was the responsibility of Abel’s father, Matthias, and without his firm but flexible hand the Bakers, who cleaned the cabins and ran the commissary, would never have known what to do. And it was only the deliberate intermingling in Recreation which his father devised that brought the Peters and Bakers together, or each family would have stayed indefinitely in its own cabins.

Lastly, there was Dr Francis. He didn’t belong to any of the three clans. Sometimes Abel asked himself where Dr Francis had come from, but his mind always fogged at a question like that, as the conditioning blocks fell like bulkheads across his thought trains (logic was a dangerous tool at the Station). Dr Francis’ energy and vitality, his relaxed good humour — in a way, he was the only person in the Station who ever made any jokes were out of character with everyone else. Much as he sometimes disliked Dr Francis for snooping around and being a know-all, Abel realized how dreary life in the Station would seem without him.

Dr Francis closed the door of his cabin and gestured Abel into a seat. All the furniture in the Station was bolted to the floor, but Abel noticed that Dr Francis had unscrewed his chair so that he could tilt it backwards. The huge vacuum-proof cylinder of the doctor’s sleeping tank jutted from the wall, its massive metal body able to withstand any accident the Station might suffer. Abel hated the thought of sleeping in the cylinder — luckily the entire crew quarters were accident-secure — and wondered why Dr Francis chose to live alone up on A-Deck.

‘Tell me, Abel,’ Dr Francis began, ‘has it ever occurred to you to ask why the Station is here?’

Abel shrugged. ‘Well, it’s designed to keep us alive, it’s our home.’

‘Yes, that’s true, but obviously it has some other object than just our own survival. Who do you think built the Station in the first place?’

‘Our fathers, I suppose, or grandfathers. Or their grandfathers.’

‘Fair enough. And where were they before they built it?’

Abel struggled with the reductio ad absurdum. ‘I don’t know, they must have been floating around in mid-air!’

Dr Francis joined in the laughter. ‘Wonderful thought. Actually it’s not that far from the truth. But we can’t accept that as it stands.’

The doctor’s self-contained office gave Abel an idea. ‘Perhaps they came from another Station? An even bigger one?’