‘No. You betrayed me, too. You ran, and you kept running, and now you’ve come full circle. I thought I would be spared. I thought the angel would pass over me. But he hasn’t, has he? That’s why you’re here.’

‘I’m not going to hurt you, Rachel. That’s not why I’m here. I didn’t kill Doc. I didn’t kill Amos. Whatever that means,’ I pointed at the wall, ‘that’s what murdered them. Not me. Whoever gunned them down was looking for it, for you.’

She collapsed to her knees, and then sank to the floor, hair spilling about her head in a ragged black halo at my feet.

I reached down and took her by the bicep, and for the first time we touched. I pulled her to her feet and tried to think straight, through the pain and exhaustion.

‘Listen. Listen to me. What was on the note? What does it really mean? You have to tell me.’

She wrested her arm loose and unstuck the hair from her face. She wiped her eyes with her fingers and sucked the tears from her lips.

‘It’s everything,’ she said. She was looking directly at me, eyes wet and wide. ‘All my work. It’s all written there, in the numbers and letters. It’s a key.’

‘What does it unlock?’

‘An algorithm. One simple algorithm.’ I thought of Baaz, our conversation in Paris. I hoped that he was safe, that the banknote was safe; that Talia had come through for him.

‘It’s for a quantum computer, isn’t it?’

She nodded. ‘It’s the ghost in the machine.’

‘And you’ve given this to the Russians? This algorithm?’

She shook her head. ‘Moshe hid it from them on the note. It would take a genius to crack it. Amos took it to the only person I could trust.’

‘But you did this for the Russians?’

‘No. It’s not like that. You wouldn’t understand. I did it because … because I had to. People dream of revolution, of the Second Coming, of Aharit Hayamim, of … whatever.’

All the bombs, I thought. People dream of all the bombs.

‘It’s everything,’ she said, ‘and I did it for everyone. It’s beautiful and invulnerable. No cryptosystem could withstand it. And the Russians paid the price.’

‘No,’ I said. ‘Doc paid the price. Amos, too. And Moshe. Shot through the heart because of that hundred-dollar bill. I didn’t pull the trigger. Not me. Not this time. All this – all this blood – for what? An equation? It’s madness. And it’s over. We’ve all paid. Them, you, me. Now let’s get out of here while we can.’