‘Oh.’

‘For trying to kill Hitler in fact, which makes me think rather highly of the chap. Take a look at this.’

The second photograph showed the younger Planck standing with a man in suit and overcoat. Blurred though the background was, the black hooked cross was obvious: a Hakenkreuz, centre of a hanging Swastika. Wartime Germany or occupied Europe was the photograph’s setting. She had no problem recognizing the other man.

‘When I met him before the war,’ she said, ‘he told me his name was Dmitri Shtemenko, though he introduced himself to everyone else as … Jürgen. Oh, what was …? Jürgen Schäffer-Braun, that was it. He was … But you know what he was, don’t you?’

‘I do.’ Rupert re-crossed his legs, elegant as always. ‘When you debriefed in Baker Street to Brian’ – he paused, just a little – ‘that night we apprehended those two darkness-driven men in Trafalgar Square … You gave those names then, Shtemenko and Schäffer-Braun, when you talked about your past.’

‘Well, then.’

It was a way of asking him to explain.

‘There was an incident in Berlin last month,’ he said. ‘During de-Nazification procedures, someone made an accusation against our man here.’ He tapped the picture of Dmitri. ‘He’d resurrected the Schäffer-Braun identity, presumably in a hurry, which is how he got flagged up. He featured in Berlin Station’s reports because of the rather unusual way he slipped out of their grasp.’

‘Using something like hypnotism,’ said Gavriela.

‘Exactly.’

She handed him back the photographs.

‘But this wasn’t why you came here?’

‘No, I just wanted confirmation of our slippery friend’s identity. In case he reappears someday.’

‘All right.’

‘Er … Would you mind if I use the little boy’s room?’

‘Go ahead.’

She cleared the cups and plates while he was gone. There was a thump – Rupert had pulled the chain unnecessarily hard – and he waited with the door closed before the sound of flushing diminished – how very like him – before exiting the lavatory and going in to the bathroom to wash his hands.

Gavriela checked on Carl: asleep, tired out by his day.

She went back to the sitting-room and sat down, knowing that Rupert on his return was going to come to the point.

Afterwards, for all her resolution against it, she went back into Carl’s room and woke him.

‘Sorry,’ she said. ‘I couldn’t help it.’

‘Ugh … That’s all right, Mummy.’ Sleepy smile, trusting eyes. ‘All right.’

‘I wondered … How would you like to live in a new place? Go to a new school?’

Carl frowned. School was new. What else could it be?

‘I mean a different new school,’ Gavriela added.

But Carl was blinking, yawning.

‘Go back to sleep,’ she told him. ‘Go on now. Mummy’s sorry. Sleep now.’

She used the voice tone she had read about in D.A.R. Greene’s book on mesmerism, but it was probably exhaustion that dropped her tired son back into sleep.

Four weeks later, she took a bus then walked along a drab street in Eastcote, the sooty air typical of Middlesex, or northwest London if one preferred. After tomorrow, there would be special transport she could ride on, so she had been told: a grey-painted coach that looked like a factory bus for ferrying workers to its site; and that had a certain accuracy.

Am I doing the right thing?

She would miss the boys, but she knew what she was good at, and here she could achieve so much more, if it was anything like she imagined.

‘There’s a list of names, old thing,’ Rupert had told her, ‘of those who worked at BP. It won’t be published for thirty years, of course, under the usual rules.’

Three decades was too long to worry about. The annual declassification of thirty-year-old secrets was nothing that could concern her.

‘And of course, there are quite a few chaps with clearance to read the list right now,’ added Rupert. ‘You’d expect that, naturally.’

‘I suppose so,’ she had said.

‘The thing is, if one compares the number of names on the list with the known complement of the Park, well, there’s something of a shortfall. A four-digit shortfall.’

Perhaps it was the reference to numbers or the hint of a mystery, but that was the moment she had become interested.

‘What happened to them all?’ she asked.

‘They never left, of course.’

‘But Bletchley Park—’

‘The site’s been decommissioned, but it’s not the location that’s important, is it?’

‘No, of course not.’ Now she understood the decision he was after. ‘Did you think I might say no? So long as you realize I don’t speak Russian.’

‘I’m sure you can learn, old girl.’

Now, she arrived at a gateway between a wall and a brick building with barred windows. In the courtyard beyond, a single-storey whitewashed affair stood before a two-storey backdrop, the whole site looking like the headquarters for one of the big dairy companies or some such, except that here no fleet of milk-carts would be setting out at dawn for the doorsteps of Middlesex. Overt signs of armed guards were absent; but the men at the gate had the relaxed, joking, watchful manner of grizzled NCOs, fazed by nothing.

‘It’s my first day,’ she said, as they checked her name off a list in the security hut. ‘I suppose someone needs to meet me.’

‘Too true, lass,’ replied a heavyset guard.

‘Aye ‘appen,’ said someone else, aping the Yorkshire accent. ‘Lucky I’m here, then.’

It was Brian, of course. The suit was of better cut than she had seen him in last; the empty left sleeve was tucked in to the pocket as if sewn in place and ironed flat. When he looked at her, no emotional spark leapt between them.

Good.

There had been nothing to worry about.

And when he added, ‘Welcome to GCHQ. Or rather, welcome back,’ his tone was only marginally warmer than neutral, mildly marking her re-entrance to the covert world.

FIFTY-SEVEN

MOLSIN 2603 AD

The maths was more painful than the fighting.

‘I can’t do this.’ Roger minimized the holo display. ‘Really, I can’t.’

They were sitting cross-legged on the quickglass floor, facing each other. Without the holo phase space and subsidiary equations glowing in mid-air, their mutual view was unobstructed.

‘It’s only a form of fear that holds you back,’ she said. ‘Are you open to a motivational technique?’

‘What kind of technique?’ he asked.

‘There are all sorts of mental states we can usefully distinguish.’ Reflected lights slid across Rhianna’s polished-jet eyes. ‘Being lost in a holodrama – very trance-like – or fascinated by abstract geometry or fearfully aware of physical danger. They’re all useful states in context, all worth triggering when appropriate. Agreed?’

‘Er, yes.’

Roger had grown wary of agreeing with her. It seemed to indicate a short path to a situation he was not going to like.

‘So here’s my psychological technique,’ said Rhianna, ‘for encouraging you to become fascinated with maths. All right?’

‘Um, OK.’

‘You’re ready for this technique?’

Saliva was doing odd things inside his throat.

‘I … Right.’

‘Brace yourself. Here it is.’

He held himself ready.

‘If you don’t solve the Lockwood equations,’ said Rhianna, ‘I will beat the fucking shit out of you.’

‘Er …’

Her knuckles cracked as she made fists.

‘Are we motivated yet?’

They were four days into the training. Roger checked through the inverse-power-law high-connection web that modelled the surveillance network Rhianna was tapped into – not just in Deltaville and Barbour, but in other sky-cities. It was a robust set-up, and he told her so.

‘But we haven’t caught sight of Helsen, have we?’ said Rhianna. ‘What do you think that means?’

‘That she’s not stupid. Specifically’ – he knew Rhianna would want an explanation – ‘she’s done the same kind of analysis, matching surveillance coverage to connectedness, and exploited the, er, dark areas. The places no one watches.’