'He's awake,' he heard her say. 'I think it worked. So that's Aethelmaer's Codex sent back, Josef.' She glanced away; Ben saw the curve of her neck, the supple muscles above the collar of her uniform. 'Step one complete. Come on, man, show a bit of enthusiasm. We have changed history – again!'

Ben's vision was misty, blurred by drugs and dusty glass. Beyond Julia he could see the calculating machine, a wall of glistening metal and wire, and the hunched figure of Josef Trojan before a flickering grey screen. There was another man too, in a dark blue uniform, sitting silent in a chair Ben was shocked to recognise George Tanner.

'You might explain that to the Allied units who are even now besieging Richborough,' Trojan said. 'Whatever we've done hasn't made a blind bit of difference, any more than the Menologium did.'

'You know very well this is a two-part process. We have sent back the weapons; we must still send back the motivator, the Testament of Eadgyth. Then it will be done – America defeated before it is spawned. Kamen just needs a bit of time to get the drugs flushed out of his system and a brush-up from the mnemonic tapes before we send him under again.'

'We may not have the time.' He sounded panicky. 'We have rushed this programme, rushed to complete the research, the calculations. And now it comes down to this, the last hours, and still it is not done-'

'I can't believe you're drinking. At a moment like this!'

'It is our last bottle of the Fuhrerwein. A gift from the Fuhrer to Himmler on his birthday, and from Himmler to me. Drink, drink! Do you want to leave it for the English? Maybe your pet policeman lover-hostage would like some too. Or Ben Kamen!'

'Try to conceal your cowardice,' Julia said. 'You know, Josef, the only thing I ever admired about you, the only thing, was your brashness. The way you used to bully your brother pointlessly – I liked that. I saw something of me in you, I suppose. Now you merely disgust me. Ah, let us work; we still have that in common.' She turned back to Ben, looking into his eyes. 'The work! How marvellous it is, how intellectually bracing. Don't you agree, Ben Kamen?'

Ben, restrained and drugged, barely able to move a muscle, did his best to meet her stare. He knew what reaction she was looking for.

She knew that Ben remained convinced that changing the past was an all-or-nothing affair. Every time he was put into his drugged sleep – if the Loom worked, and he still wasn't prepared to concede that it did, that this wasn't all some foolish illusion – then he died, as all of history folded away like a crumpled bit of paper. And the Ben who had just woken had, in a sense, existed for only a few minutes, since the implementation of the change, and all his memories were of a history that was entirely new, a fabrication. This was his conviction, and it filled him with a deep existential horror.

And this hellish woman knew this. As she peered now into Ben's head she was looking for the terror that penetrated his soul. She relished it, a connoisseur of pain.

But the lab shuddered again. She still had Ben in a cage, but now it was Julia and all her projects who was under threat. He met her stare and grinned. Her face twisted into a snarl, and she turned away.

'Look at this,'Trojan said. 'The television broadcast is back! The Allies have taken over the Promi station.'

'How enterprising of them,' Julia said. 'Ah. American and British soldiers shaking hands. How convenient that there was a camera there to record the historic moment when their twin thrusts met north of Hastings… Oh, and here's Churchill, walking the cliffs of Dover – of course he would be there. The great opportunist stands amid the ruins of his country, celebrates a victory that is not his, and looks out to sea towards his next conquests. And they call Hitler a warmonger!'

'Do you think all this is a foretaste of what is to come, Julia? The resources assembled against us – is this the pattern we must endure for the rest of the war, until Americans shake hands with Russians in the ruins of Berlin?'

'You are a fool, Josef Trojan. A fool and a coward. Just remember, now that we have got this far I can finish the job myself. I don't need you. Not any more.'

'I do not forget that,' said Trojan. 'Not for a minute. Oh, look – a flyby by Spitfires. Such a pretty aircraft, don't you think?…'

Julia checked the dials on the monitors by Ben's cage. 'The specimen is ready. A few more minutes with the tapes and we can send him off on his final journey into the past.'She grinned. 'Listen well, little fellow.' Out of Ben's sight she snapped a switch.

A recorded voice began to speak in his ear. He tried not to listen, to think of other things, to empty his head. But he felt a mild sedative slide into his veins, washing away his determination, as the Testament of Eadgyth poured into his head:

In the last days

To the tail of the peacock

He will come: The spider's spawn, the Christ-bearer

The Dove…

Send the Dove east! O, send him east!

Another shuddering crash as a shell fell close, and the small-arms fire grew louder.

The Sherman tank's great gun fired one round after another into the carcass of the squat concrete tower, the central fortification of the Richborough complex. The defenders seemed to have nothing left to respond with, nothing but machine guns and rifles whose bullets rattled off the tank's oblivious carcass. The booming of the tank's gun was huge, and though Mary kept her hands clamped over her ears she could feel it in her chest, the cavities of her skull.

Mary was huddled with Gary, Willis Farjeon and the young German prisoner, Obergefreiter Ernst Trojan, in a captured trench. More troops, a total of eight in the group, rested nearby. They were waiting for Tom Mackie. The trench smelled of blood and cordite, the stink of battle.

Gary touched her shoulder. 'Mom, are you sure you're all right?' He had to yell over the sound of the gun.

'What do you think?' she shrieked back. She felt self-conscious in her 'siren suit', her blue WVS coveralls, and her pack on her back contained the results of her researches into Geoffrey Cotesford's memoir – a pack of academic documents in a war zone.

Gary said, 'I never even got to see the arch I spent a year of my life toiling over. And now they've pulled it down to build a flak tower!'

'Same thing happened to Claudius's monument. When the tide turned against Rome, they tore that down too, to build the Saxon-shore fort.'

'I guess England's not a place you want to invade,' Gary said.

Perhaps that was true, she thought. And how strange it was that today, the last moments of one immense invasion might be played out on the scene of another nineteen hundred years earlier.

Ernst Trojan stirred. He wore his grubby Wehrmacht uniform, but he had been given a British army helmet for his safety, and he had his hands tied behind his back.

Willis yelled at him, 'You OK, Fritz? Anything I can get you? How about a beer?'

'Leave him alone, Willis,' Gary said.

There was another crash, and they all ducked.

Tom Mackie came crawling along the trench. He crouched down with them, holding onto his Navy officer's hat. 'Afternoon all.'

'About bloody time,' Willis said. 'Sir.'

'We're all doing our best, Farjeon,' Mackie said, unperturbed. 'Well, we're fit to go at last,' he said to Mary. 'The boffins have arrived.'

She risked a glance out of the trench. She saw that an armoured vehicle at the rear of the field was disgorging military types and civilians, some quite elderly. 'Who are they?'

'Some of my MI-14 colleagues. There are a few chaps from Bletchley Park who want to see if the Nazis have made any improvements to their Colossus calculating machines. And some American boffins.' He pointed. 'That is John von Neumann. An egghead among eggheads. He worked at Princeton in the time of Ben Kamen and Godel. Knows more maths and physics than they did, probably. Actually we have him on loan from the Americans' atomic bomb project. And that is a man called Thomas Watson. Head of International Business Machines. You know – IBM, the big calculating-machine corporation in the States. Not terribly ethical, so the rumours go. Got a medal from Hitler.'