‘Wait until this afternoon,’ he called back. ‘You’re really going to see something.’

The floor manager at the Coliseum initialled the two passes. — ‘Students, eh? All right.’ He jerked a thumb at the long package Franz and Gregson were carrying. ‘What have you got there?’

‘It’s a device for measuring air velocities,’ Franz told him.

The manager grunted and released the stile.

Out in the centre of the empty arena Franz undid the package and they assembled the model. It had a broad fan-like wing of wire and paper, a narrow strutted fuselage and a high curving tail.

Franz picked it up and launched it into the air. The model glided for twenty feet and then slithered to a stop across the sawdust.

‘Seems to be stable,’ Franz said. ‘We’ll tow it first.’

He pulled a reel of twine from his pocket and tied one end to the nose. As they ran forward the model lifted gracefully into the air and followed them around the stadium, ten feet off the floor.

‘Let’s try the rockets now,’ Franz said. He adjusted the wing and tail settings and fitted three firework display rockets into a wire bracket mounted above the wing.

The stadium was four hundred feet in diameter and had a roof two hundred and fifty feet high. They carried the model over to one side and Franz lit the tapers.

There was a burst of flame and the model accelerated across the floor, two feet in the air, a bright trail of coloured smoke spitting out behind it. Its wings rocked gently from side to side. Suddenly the tail burst into flames. The model lifted steeply and looped up towards the roof, stalled just before it hit one of the pilot lights and dived down into the sawdust.

They ran across to it and stamped out the glowing cinders. ‘Franz!’ Gregson shouted. ‘It’s incredible! It actually works.’

Franz kicked the shattered fuselage. ‘Of course it works,’ he said impatiently. ‘But as Sanger said, what’s the point of it?’

‘The point? It flies! Isn’t that enough?’

‘No. I want one big enough to hold me.’

‘Franz, slow down. Be reasonable. Where could you fly it?’

‘I don’t know,’ Franz said fiercely. ‘But there must be somewhere!’

The floor manager and two assistants, carrying fire extinguishers, ran across the stadium to them.

‘Did you hide the matches?’ Franz asked quickly. ‘They’ll lynch us if they think we’re Pyros.’

Three afternoons later Franz took the elevator up 150 levels to 677-98, where the Precinct Estate Office had its bureau.

‘There’s a big development between 493 and 554 in the next sector,’ one of the clerks told him. ‘I don’t know whether that’s any good to you. Sixty blocks by twenty by fifteen levels.’

‘Nothing bigger?’ Franz queried.

The clerk looked up. ‘Bigger? No. What are you looking for — a slight case of agoraphobia?’

Franz straightened the maps spread across the counter. ‘I wanted to find an area of more or less continuous development. Two or three hundred blocks long.’

The clerk shook his head and went back to his ledger. ‘Didn’t you go to engineering school?’ he asked scornfully. ‘The City won’t take it. One hundred blocks is the maximum.’

Franz thanked him and left.

A south-bound express took him to the development in two hours. He left the car at the detour point and walked the three hundred yards to the end of the level.

The street, a seedy but busy thoroughfare of garment shops and small business premises running through the huge ten-mile-thick B. I. R. Industrial Cube, ended abruptly in a tangle of ripped girders and concrete. A steel rail had been erected along the edge and Franz looked down over it into the cavity, three miles long, a mile wide and twelve hundred feet deep, which thousands of engineers and demolition workers were tearing out of the matrix of the City.

Eight hundred feet below him unending lines of trucks and railcars carried away the rubble and debris, and clouds of dust swirled up into the arc-lights blazing down from the roof. As he watched, a chain of explosions ripped along the wall on his left and the whole face slipped and fell slowly towards the floor, revealing a perfect cross-section through fifteen levels of the City.

Franz had seen big developments before, and his own parents had died in the historic QUA County cave-in ten years earlier, when three master-pillars had sheared and two hundred levels of the City had abruptly sunk ten thousand feet, squashing half a million people like flies in a concertina, but the enormous gulf of emptiness still stunned his imagination.

All around him, standing and sitting on the jutting terraces of girders, a silent throng stared down.

‘They say they’re going to build gardens and parks for us,’ an elderly man at Franz’s elbow remarked in a patient voice. ‘I even heard they might be able to get a tree. It’ll be the only tree in the whole county.’

A man in a frayed sweat-shirt spat over the rail. ‘That’s what they always say. At a dollar a foot promises are all they can waste space on.’

Below them a woman who had been looking out into the air started to simper nervously. Two bystanders took her by the arms and tried to lead her away. The woman began to thresh about and an F. P. came over and pulled her away roughly.

‘Poor fool,’ the man in the sweat-shirt commented. ‘She probably lived out there somewhere. They gave her ninety cents a foot when they took it away from her. She doesn’t know yet she’ll have to pay a dollar ten to get it back. Now they’re going to start charging five cents an hour just to sit up here and watch.’

Franz looked out over the railing for a couple of hours and then bought a postcard from one of the vendors and walked back to the elevator: He called in to see Gregson before returning to the student dormitory. The Gregsons lived in the West millions on 985th Avenue, in a top three-room flat right under the roof. Franz had known them since his parents’ death, but Gregson’s mother still regarded him with a mixture of sympathy and suspicion. As she let him in with her customary smile of welcome he noticed her glancing at the detector mounted in the hall.

Gregson was in his room, happily cutting out frames of paper and pasting them on to a great rickety construction that vaguely resembled Franz’s model.

‘Hullo, Franz. What was it like?’

Franz shrugged. ‘Just a development. Worth seeing.’

Gregson pointed to his construction. ‘Do you think we can try it out there?’

‘We could do.’ Franz sat down on the bed. He picked up a paper dart lying beside him and tossed it out of the window. It swam into the street, lazed down in a wide spiral and vanished into the open mouth of the ventilator shaft.

‘When are you going to build another model?’ Gregson asked.

‘I’m not.’

Gregson looked up. ‘Why? You’ve proved your theory.’

‘That’s not what I’m after.’

‘I don’t get you, Franz. What are you after?’

‘Free space.’

‘Free?’ Gregson repeated.

Franz nodded. ‘In both senses.’

Gregson shook his head sadly and snipped out another paper panel. ‘Franz, you’re mad.’

Franz stood up. ‘Take this room,’ he said. ‘It’s twenty feet by fifteen by ten. Extend its dimensions infinitely. What do you find?’

‘A development.’

‘Infinitely!’

‘Non-functional space.’

‘Well?’ Franz asked patiently.

‘The concept’s absurd.’

‘Why?’

‘Because it couldn’t exist.’

Franz pounded his forehead in despair. ‘Why couldn’t it?’

Gregson gestured with the scissors. ‘It’s self-contradictory. Like the statement "I am lying". Just a verbal freak. Interesting theoretically, but it’s pointless to press it for meaning.’ He tossed the scissors on to the table. ‘And anyway, do you know how much free space would cost?’

Franz went over to the bookshelf and pulled out one of the volumes. ‘Let’s have a look at your street atlas.’ He turned to the index. ‘This gives a thousand levels. KNI County, one hundred thousand cubic miles, population 30 million.’