I went back into the priest’s house. Rachel had sat down again, huddled on the floor, fixated trance-like on the candles. I raised the phone and took a photograph of the calculations scrawled across the wall. Then I removed the battery and put the phone back in my pocket. Moshe would have approved: it doesn’t hurt to have insurance. I walked over to her and touched her gently on the shoulder.

‘It’s time to go.’ She shook her head and kept her back turned to me. ‘Rachel, please. We need to leave now.’

I circled around and stood in front of her.

‘I can’t,’ she said, looking up at me.

‘We can make it, Rachel. We can get over the border. My people will meet us, they’ll help us. It’s a long drive, but we can do it. We can give them the algorithm. You can continue your work.’ Her eyes widened. ‘It will be a memorial to Doc, to Amos. Finish what you started. You can do it. We can do it. But first we have to leave.’

She scuttled away from me, terrified.

‘No.’

‘Rachel, please. Trust me. Everything’s going to be all right.’

‘You can’t give it to them, Max. You can’t. It has to be destroyed. You can’t give it to anyone.’

‘It’s OK, I promise. I won’t.’

She backed away further, fingernails clawing at the wooden floorboards.

‘I don’t believe you. You did kill my father. That’s why you’re here. You’ve got the algorithm, and once you understand it you’ll get rid of me. You and Avilov. You’re the same. You’re all the same.’

I bridled at the thought of it. But she was right. Frank Knight and Leonid Avilov had something else in common, too: an individual – any individual – would always be expendable in the face of their ambition, whether that be serving the interests of national security or their own personal advancement.

‘Avilov is dead,’ I said.

‘It doesn’t matter. The Russians have the computer.’

‘Let them build it. Without you it will only be a dream. No ghost for their machine, hey?’ I fished the fake Arkhangel bill from my pocket. I unfolded it and then opened the stove door. The embers inside flared with the rush of air. I held the note up so she could see it, see my near-perfect interpretation of her sloppy, Cyrillic script on the reverse. ‘Forget London. We’ll go east, deep into the forest. Not even your angel will be able to find us. We’ll survive. Thrive. You and me.’ And then I held the note over the grate and let the flames take it. ‘There,’ I lied. ‘It’s over.’ I walked back to the candles, to the wall she’d used as a blackboard. ‘And this is the algorithm, too?’

‘Yes,’ she nodded. ‘Part of it. The final part.’