‘There’s a cave-in down at KEN County! Fifty blocks by twenty by thirty levels.’

‘Listen to this — “PYROMANIACS STAGE MASS BREAKOUT! FIRE POLICE CORDON BAY COUNTY!”

‘It’s a beautiful counter. Detects up to .005 per cent monoxide. Cost me three hundred dollars.’

‘Have you seen those new intercity sleepers? They take only ten minutes to go up 3,000 levels!’

‘Ninety cents a foot? Buy!’

‘You say the idea came to you in a dream?’ the voice snapped. ‘You’re sure no one else gave it to you.’

‘No,’ M. said. A couple of feet away from him a spot-lamp threw a cone of dirty yellow light into his face. He dropped his eyes from the glare and waited as the sergeant paced over to his desk, tapped his fingers on the edge and swung round on him again.

‘You talked it over with your friends?’

‘Only the first theory,’ M. explained. ‘About the possibility of flight.’

‘But you told me the other theory was more important. Why keep it from them?’

M. hesitated. Outside somewhere a trolley shunted and clanged along the elevated. ‘I was afraid they wouldn’t understand what I meant.’

The sergeant laughed. ‘Do you mean they would have thought you really were insane?’

M. shifted uncomfortably on the stool. Its seat was only six inches off the floor and his thighs felt like slabs of inflamed rubber. After three hours of cross-questioning logic had faded. ‘The concept was a little abstract. There weren’t any words for it.’

The sergeant shook his head. ‘I’m glad to hear you say it.’ He sat down on the desk, watched M. for a moment and then went over to him.

‘Now look,’ he said confidentially. ‘It’s getting late. Do you still think both theories are reasonable?’

M. looked up. ‘Aren’t they?’

The sergeant turned to the man watching in the shadows by the window. ‘We’re wasting our time,’ he snapped. ‘I’ll hand him over to Psycho. You’ve seen enough, haven’t you, Doctor?’

The surgeon stared at his hands. He had taken no part in the interrogation, as if bored by the sergeant’s method of approach.

‘There’s something I want to find out,’ he said. ‘Leave me alone with him for half an hour.’

When the sergeant had gone the surgeon sat down behind the desk and stared out of the window, listening to the dull hum of air through the ventilator shaft which rose out of the street below the station. A few roof lights were still burning and two hundred yards away a single policeman patrolled the iron catwalk running above the street, his boots ringing across the darkness.

M. sat on the stool, elbows between his knees, trying to edge a little life back into his legs.

Eventually the surgeon glanced down at the charge sheet.

‘Tell me about this dream,’ he said, idly flexing a steel rule between his hands as he looked across at M.

‘I think you’ve heard everything, sir,’ M. said.

‘In detail.’

M. shifted uneasily. ‘There wasn’t much to it, and what I do remember isn’t too clear now.’

The surgeon yawned. M. waited and then started to recite what he had already repeated twenty times.

‘I was suspended in the air above a flat stretch of open ground, something like the floor of an enormous arena. My arms were out at my sides, and I was looking down, floating—’ ‘Hold on,’ the surgeon interrupted. ‘Are you sure you weren’t swimming?’

‘No,’ M. said. ‘I’m certain I wasn’t. All around me there was free space. That was the most important part about it. There were no walls. Nothing but emptiness. That’s all I remember.’

The surgeon ran his finger along the edge of the rule.

‘Go on.’

‘Well, the dream gave me the idea of building a flying machine. One of my friends helped me construct it.’

The surgeon nodded. Almost absently he picked up the charge sheet and crushed it with a single motion of his hand.

‘Don’t be absurd, Franz!’ Gregson remonstrated. They took their places in the chemistry cafeteria queue. ‘It’s against the laws of hydrodynamics. Where would you get your buoyancy?’

‘Suppose you had a rigid fabric vane,’ Franz explained as they shuffled past the hatchways. ‘Say ten feet across, like one of those composition wall sections, with hand grips on the ventral surface. And then you jumped down from the gallery at the Coliseum Stadium. What would happen?’

‘You’d make a hole in the floor. Why?’

‘No, seriously.’

‘If it was large enough and held together you’d swoop down like a paper dart.’

‘Glide,’ Franz said. ‘Right.’ Thirty levels above them one of the intercity expresses roared over, rattling the tables and cutlery in the cafeteria. Franz waited until they reached a table and sat forward, his food forgotten.

‘And say you attached a propulsive unit, such as a battery-driven ventilator fan, or one of those rockets they use on the Sleepers. With enough thrust to overcome your weight. What then?’

Gregson shrugged. ‘If you could control the thing, you’d, you’d…’ He frowned at Franz. ‘What’s the word? You’re always using it.’

‘Fly.’

‘Basically, Matheson, the machine is simple,’ Sanger, the physics lector, commented as they entered the science library. ‘An elementary application of the Venturi Principle. But what’s the point of it? A trapeze would serve its purpose equally well, and be far less dangerous. In the first place consider the enormous clearances it would require. I hardly think the traffic authorities will look upon it with any favour.’

‘I know it wouldn’t be practical here,’ Franz admitted. ‘But in a large open area it should be.’

‘Allowed. I suggest you immediately negotiate with the Arena Garden on Level 347-25,’ the lector said whimsically. ‘I’m sure they’ll be glad to hear about your scheme.’

Franz smiled politely. ‘That wouldn’t be large enough. I was really thinking of an area of totally free space. In three dimensions, as it were.’

Sanger looked at Franz curiously. ‘Free space? Isn’t that a contradiction in terms? Space is a dollar a cubic foot.’ He scratched his nose. ‘Have you begun to construct this machine yet?’

‘No,’ Franz said.

‘In that event I should try to forget all about it. Remember, Matheson, the task of science is to consolidate existing knowledge, to systematize and reinterpret the discoveries of the past, not to chase wild dreams into the future.’

He nodded and disappeared among the dusty shelves.

Gregson was waiting on the steps.

‘Well?’ he asked.

‘Let’s try it out this afternoon,’ Franz said. ‘We’ll cut Text 5 Pharmacology. I know those Fleming readings backwards. I’ll ask Dr McGhee for a couple of passes.’

They left the library and walked down the narrow, dimly-lit alley which ran behind the huge new civil engineering laboratories. Over seventy-five per cent of the student enrolment was in the architectural and engineering faculties, a meagre two per cent in pure sciences. Consequently the physics and chemistry libraries were housed in the oldest quarter of the university, in two virtually condemned galvanized hutments which once contained the now closed philosophy school.

At the end of the alley they entered the university plaza and started to climb the iron stairway leading to the next level a hundred feet above. Halfway up a white-helmeted F. P. checked them cursorily with his detector and waved them past.

‘What did Sanger think?’ Gregson asked as they stepped up into 637th Street and walked across to the suburban elevator station.

‘He’s no use at all,’ Franz said. ‘He didn’t even begin to understand what I was talking about.’

Gregson laughed ruefully. ‘I don’t know whether I do.’

Franz took a ticket from the automat and mounted the down platform. An elevator dropped slowly towards him, its bell jangling.