Run now, my darling.

She nodded, and made her way up the steps. Once out of sight, she would have to move fast.

Gérard said, ‘We’ve made up a new batch of leaflets. We need to think about whether to place them around the Old Town again, or go further afield.’

Wahlberg was smiling in a way that Erik did not like.

You’re a creature of the darkness. Are you a Nazi too?

The one other man he had met like this, Dmitri Shtemenko, had been a Bolshevik agent who had saved Gavriela’s life – his sister, who might be alive or dead and he would never know.

‘Leaflets.’ Wahlberg’s expression was half-smile, half-sneer. ‘I thought this group did more than leave seditious bits of paper lying around.’

‘It’s a bullet in the head regardless,’ said Gérard.

Wahlberg was holding Erik’s stare.

‘Kill him,’ said Erik, addressing Gérard.

‘What?’

But a crash from upstairs meant the opportunity had passed. Boots clattered, louder as they neared the cellar stairs.

Knowing exactly which way to come.

They had breakfast in a Lyons Tea House in Kilburn where noise bounced off the ceiling in the steamy atmosphere, filled with the cheerful clatter of cutlery and the chatting of the clientele; and if it were not for the tape criss-crossing the windows and the number of people in uniform, you might have thought it was peacetime.

Rupert sat with his legs crossed. Brian had pushed his chair a little way back from the table. Gavriela tried to read the unspoken context of their conversation before her arrival, and failed. From the questions they had asked in debriefing, Brian had not known about the message that she had decrypted, but Rupert possibly had. Did that mean it had been planted for her to act on?

Alone with Brian, there had been no discussion of her actions, beyond his comforting her in the aftermath of shock. And the lovemaking, rough and urgent and a surprise to them both.

‘Last night’s shenanigans,’ said Rupert now, ‘weren’t what anyone expects, not here.’

Their language had to remain oblique, because of eavesdroppers; but they were far enough from Baker Street that no SOE personnel were likely to be here, and Gavriela thought that was deliberate.

‘Am I in trouble?’ What she wanted to ask was, were they were going to arrest her? ‘Because of what happened?’

Brian’s face tightened. She hoped it meant he would fight her cause.

‘Considering what you prevented,’ said Rupert, ‘you’re a heroine, and that’s exactly how you’ll be described in our reports.’

She did not feel like a heroine. Nor did she imagine his report mentioned hypnosis of a kind that no psychologist would recognize. But so long as the four guards were not blamed, she did not see how twisting the truth could matter, not in a file that few people would ever read.

‘Too bad we got nothing from the blighter.’ Rupert shrugged his elegant shoulders. ‘But nostra culpa, not yours, don’t you see?’

‘Gabby did a good job.’ Brian’s pale face began to colour. ‘More than anyone could expect.’

‘Indeed.’ Now the raised eyebrow. ‘I believe that’s what I just said.’

Rupert’s manner was beginning to annoy Gavriela, but she quelled the feeling. If this was provocation, it was likely to be deliberate. Bletchley Park had its share of chess grandmasters, but Rupert played all of life as if it were a game.

‘And this is not the first such person’ – Rupert’s searchlight gaze swung to her – ‘you’ve come across, is that right?’

‘There was a man called Dmitri in Berlin, as I told Brian. Plus a Nazi rabble-rouser, once.’

She did not want to say anything about the man’s identity, partly because she needed Rupert to believe her sane, partly because she did not want to give the appearance of an excuse to a murderous psychotic whose power derived from a conscious understanding of mass psychology and practised oratory as much as inductive hallucination. Or so she believed.

‘So they’re not all Nazis, then.’ Rupert pronounced it in the Churchillian manner: nah-zees. ‘Are you saying they’ve an agenda of their own? Or are they separate individuals who just happen to manifest similar odd attributes?’

Gavriela blinked. So did Brian.

He’s taking it seriously.

You would think Rupert had considered this over an extended period of time. Then again, he would have studied Nazi mysticism, to the extent that it drove the regime’s plans for conquest.

‘I don’t know,’ she said. ‘Separate, I think … But it’s a feeling, no more.’

‘Well, regardless.’ Rupert lowered his voice. ‘I’m driving to BP this morning. I’ll give you a lift.’

Brian said, ‘There’s no way I can get back, with this thing I’m seconded to.’ He looked at Gavriela. ‘I’ll see you next week, most likely.’

‘I’ll … see you then.’

Did she want to kiss him? In public, without Rupert’s presence, she thought the answer might have been yes. As it was, her movements felt shut down, her body tight.

As they left the tea-house, both men donned their hats and nodded to each other. Then Rupert took Gavriela’s arm, and they walked off in one direction, while Brian went the other way.

I don’t know how I’m supposed to feel.

Something that happened far too often in her life.

No one said anything the next day in Hut 27: nothing about signals regarding some darkness, nothing about Gavriela’s trip to London. Clive had returned, and was working on new intercepts with no mention of half-finished work from days before. During a break when Gavriela happened – by apparent chance – to find herself alone in the room, she hovered by Clive’s desk but did not open the drawer.

They had given her a second chance. She needed to take it.

That night she walked back into Bletchley village with Rosie, who chatted about the trivia of her day. Gavriela, in the back of her mind, was ruminating on maths the way physicists often do: wondering at the way the right mathematical tools so often existed in advance of science finding a reason for using them, meaning mathematicians had explored such lofty abstract thought-spaces with no original connection to reality. Here in BP she had witnessed feats of mathematical reasoning – counter-intuitive statistics, rigorous Boolean logic, the depths of group theory – that she would find hard to explain to an outsider, even if she were allowed. But Rosie kept her grounded in reality.

‘I had a letter from Jack yesterday! It was there when I got home last night.’

‘That’s great, Rosie. Is he all right?’

‘He’s fine, and getting a tan, he says.’ Rosie took out a small, lace-edged handkerchief, waving it in the gloom. ‘Got my initials, see?’

There might have been a curlicued RD, but the night was too dark to be sure.

‘Jack bought the hankie on leave, and sent it—’

Rosie dabbed at one eye.

‘He says we’ll get married when he’s home.’

‘Oh, Rosie.’

They both stopped. Gavriela hugged her.

‘He’ll be OK,’ she said. ‘He’ll be OK.’

But they both knew, in the sudden randomness of wartime, that letters from servicemen took time to arrive, and sometimes the sender was already dead or maimed when their sweetheart read those cheery words.

Rosie stepped back, sniffing.

‘Now all we need,’ she said, ‘is to get you a nice young gentleman, and we’ll be sorted.’

‘Maybe,’ said Gavriela.

They walked on, while she remembered the overwhelming lust for coupling that overtook her in the Tube station and the night that followed, all of it dislocated from her normal world; and she wondered whether it was romance or something more primal, and whether that made a difference.

‘How about a nice cup of acorn tea?’ Rosie’s place was close, not quite on Gavriela’s way home, but near enough. ‘I’ve got a book you can borrow. I didn’t finish it myself, but you might like it.’