‘How do you mean?’

‘The banknote wasn’t complete,’ she said, turning to look at the calculations writ large behind her. ‘It took coming here finally to see it, to finish it.’

‘So, this is the conclusion?’

She nodded again.

‘It gives Azrael the eyes to see.’

‘The hundred-dollar bill and this,’ I pointed at the wall, ‘are, were, the only copies?’

‘Yes, but …’

I paced back to the stove and picked up her sleeping bag.

‘And Amos, could he have told anyone?’

‘No. He didn’t know how close I was to solving it.’

‘And Doc, what did Doc know?’

‘He knew I’d made a breakthrough, but … Max, what are you doing?’

She watched me as I picked up a candle and held it under the sleeping bag. The nylon sacking caught almost immediately. I swung the growing ball of fire under the dresser. The old varnish cracked and blistered. Small blue flames licked up its sides and took hold of the legs. Within seconds the wood was alight, the room filling with smoke. I stepped back and covered my face as a rush of flame leapt up. Whatever had been stored inside the cabinet had accelerated the burn into a roaring blaze. Soon the floorboards would catch, then the wall and ceiling. The roof would go up and the house would come down – by which time we would be on our way.

I took her by the wrist, but she twisted free.

‘No,’ she shouted above the hiss of the fire, stepping backwards towards the flames. ‘You’re not listening. You haven’t understood anything. It isn’t the note that needs to be destroyed.’

I went after her, arms outstretched, lungs already straining from the smoke and heat.

‘Please, Rachel.’ She was choking now, struggling to draw breath as the oxygen burned out of the room. She hesitated and then let me embrace her. I held her close to my chest as the blaze began to spread across the floor. ‘It’s OK,’ I said.

She flattened her hands against my back and I readied myself to take her weight. My shoulder, ribs throbbed. She buried her face into my chest. With one hand she gripped my waist; with the other the back of my neck.

‘Just relax.’

A brilliant mind; an infuriating, captivating lover; a revolutionary – whatever she once had been was consumed then and there by madness. Perhaps completing the algorithm had sent her over the edge; perhaps it had taken the descent into insanity finally to see the answer she’d devoted a lifetime to looking for. She had spent years fighting her demons, without ever imagining that she would create one, become one. She had gazed into the abyss; and the abyss had gazed into her.