Doris asked softly, 'Is this Ben?'

He whirled around. She was looking into the glass-walled inner chamber. There was nothing much in there but a bed, he saw, with white sheets, and a table and chair and a washbasin, a piss-pot on the floor. And on the bed, over the sheets, lay a man in striped prison pyjamas, small, hunched over with his legs up by his belly, his arms folded, mussed black hair dark against the pillow. He wore a kind of cap of silvery metal, connected by the wires to a metal cabinet beside the bed. He was bathed in brilliant white light.

Gary hammered on the glass wall. 'Ben. Ben!'

The sleeping figure stirred resentfully, mumbling.

'Keep it down, for God's sake. Let's get him out of there.' The glass box had a door, a lock embedded in its transparent structure. Doris produced another tool, like a fine screwdriver, and began to work at the lock.

At last Ben opened an eye. When he saw Gary, he lurched up to a sitting position. His shirt hung open, showing his belly. He got out of bed and ran to the glass wall. The metal cap was ripped off his head by the trailing wires. His crown had been shaved, like a monk's tonsure, and his scalp was prickled by an array of crimson dots. He stood there flattened against the glass, his mouth open. 'You came for me.'

Gary was inches away, but could not touch him. 'I told you I would, didn't I? It's OK, Ben. We'll get you out of this fucking zoo. Christ, I think they've got him drugged up. His eyes-'

'Gary! Gary!'

Doris still worked at the lock. 'Try to keep him quiet.'

Gary made calming motions with his hands. 'Ben, it's OK, just take it easy.'

The door swung back soundlessly, and Doris, tucking away her lock-picking tool, hurried into the glass room. When Doris reached for him Ben flinched back, hammering his head on the glass wall. 'Christ,' Doris said. 'Gary, get in here, for God's sake.'

Gary pushed past Doris. Ben threw himself at him. 'Gary, oh my word, you came, I thought I would never, I thought…' He buried his face in Gary's chest.

Gary wrapped his arms around him. Ben felt almost podgy, with fat over his ribs and belly. 'They've been feeding you up. Christ, what have they done to you?'

Ben looked up, his eyes glazed. 'It's what they've done with me… Drugged up, asleep most of the time. Dreaming. Past and future, past and future. We're a bridge across time, a computing machine and my poor wandering psyche. You don't want to know, Gary, I mean it. Although your mother knows, I think, she might understand by now.'

'Never mind that,' Doris hissed. 'Come on. Out.'

Ben didn't want to let go of Gary, but they persuaded him to grab Gary's arm so that the two of them could walk, awkwardly, with Doris's help.

Doris, all business, shepherded them to the heap of plaster dust under the hole in the roof. 'Out the way we came. Gary, get back up there. Use that chair. I'll give Ben a boost back up. I'll follow, after I've done a bit of business in here. And then-'

'No.' Ben had been passive for a few seconds, but now he started panicking. He twisted away from them both and ran to the bank of mechanical gear at the back wall. 'I must see if they've done what they threatened, if they've done it…'

'We don't have time for this,' Doris snapped.

Gary grabbed her arm. 'Look, Doris, take it easy. He'll be a lot easier to get out through that roof space conscious than unconscious.'

She bit her lip. 'All right. But quickly.'

Ben found a paper-tape punch. He scrolled through its output, and pawed through heaps of notes, handwritten in German, some technician's orderly journal.

Gary stood by him. 'We have to go, pal.'

'Not before I know if they've used this thing.'

'For what?' Gary looked up at the bank of gleaming equipment, the relays and wires, rods and gears. It was beautiful, he thought, a beautifullymade machine in the midst of all this madness. 'What is this, Ben?'

Ben snorted. 'Actually it's a Z3. An electromechanical calculating machine. The pride of German engineering. They use it to calculate the Godel trajectories, you see, the paths back to the past. They come here, you know. Technicians from the Zuse Apparatebau in Berlin. Zuse sends technicians from Berlin to service it! Can you believe that? They get paid. And I, I must dream… Unh.' It was a grunt, as if he had been struck in the stomach.

'Ben?'

'They did it.' He held up a length of paper tape. 'See? There's the proof, right there. And the date stamp.'

'They did what?'

'They sent it back in time. The Menologium. Just two days ago. Tell your mother. Make sure she understands, that she knows. Tell her I signed it.' He grinned. 'I signed my name in their fucking Menologium. Now my name must be in the history books. Think of that! But if only you'd come earlier – it's too late, they did it again, like Rory, and I died, I died again-' And he slumped into the corner, his back to the shining machine.

'Enough,' Doris said. 'Help me, Gary.'

They each grabbed an arm and began hauling, but Ben was limp now, just a burden. He said, 'To wipe out all of history, at the push of a button, the close of a relay – billions upon billions of lives, snuffed out and swapped for a whole new set – the close of a relay – what could be more fascistic than that?'

Gary could hear noise coming from above, shouting, heavy running footsteps – the thump of an explosion somewhere, a rattle of gunfire. 'It's coming apart,' he said.

'You surprise me,' Doris said. 'We might still get out of this. Up you go.'

Gary hopped on a chair, jumped so he got his hands onto the joists, and pushed himself up. 'Pass him up.' Sitting with his legs dangling through the ceiling, he reached down with his arms.

The door slammed open. SS troopers burst in, six, eight, ten of them, all with automatic weapons or pistols. Julia Fiveash was at their head, waving a silver pistol of her own. The SS troopers screamed German phrases that Gary knew well from the stalag: 'Down!' 'On your knees, on the floor!'

Doris looked up at Gary. Ben was slumped in her arms, almost unconscious. She mouthed, 'Go!' And suddenly she had her knife at Ben's throat.

Gary lifted his legs out of the hole and scrambled back.

Doris turned to face Fiveash. 'Back off, you traitorous bitch, or I cut his throat!'

The troopers hung back uncertainly.

Fiveash advanced, step by step, her pistol held out straight before her in her two hands. 'I knew there was something wrong with you people. The way the Woolers greeted each other – that was more than a mother greeting her prisoner son – I knew there was an agenda! I admit I didn't spot you, Silver-'

With a grunt Doris shoved Ben at Fiveash. He fell against her, tangling her up. And Doris ran at the big calculating machine, the Z3. Fiveash yelled at the troopers.

Suddenly Gary saw what Doris was going to do. He ducked behind a roof joist for cover.

The explosion was a pulse of light, the concussion a punch in the gut. Over the Z3 the roof plaster blew upwards, and Gary tried to shield his face.