London grumbled around them. A siren, sharp, wailed along the edge of the park. Ed watched the blue lights skitter along, safe and threatening all at once.

Ed cleared his throat, spoke quickly. ‘Some nights, the Afghans would go to one of the villages nearby. They would go there . . . and snatch one of the little boys . . . They would grab one, and . . .’ He forced himself to carry on. ‘At night, we could hear the little boys screaming, out in the darkness.’

Casey sat in silence, watching the lights flicker over the city.

‘They raped them. The boys . . .’

‘Oh, Ed.’

‘Don’t.’

‘What did you . . .’

‘We didn’t do anything. We just listened. One night, we had a bonfire going all jolly. Some of my men were singing, and when they stopped . . . When they stopped, we could hear this little boy crying out beyond the circle of light.’

A plane tracked across the sky towards Heathrow. Casey’s eyes followed it aimlessly.

‘But what could you have done?’ she asked quietly.

‘I don’t know. We didn’t know. We had a job. Orders. These were our allies . . .’ His voice hardened. ‘In the morning, the Afghans would be all bright and breezy. As if it was normal, just what they did. And maybe it was. And we needed them. We were miles from anywhere else. We needed them, and they knew that.’

‘I’m sorry.’

‘Sorry for who?’ He still had his back to her. ‘Bacha bazi, that’s what they called it. Boy play. We just looked the other way.’

Across the park, London spiked into the sky. The Shard, the Gherkin, the BT Tower, tens of millions of lives.

‘We didn’t do anything,’ Ed said tightly. ‘We just got on with it.’

‘It wasn’t your fault.’ The words were automatic.

‘And then when we went out to Salama together,’ he spoke very quietly, ‘again, you and I. We just watched. We didn’t do anything . . .’

‘I’m sorry,’ Casey said. ‘So sorry. I didn’t know.’

He spun round towards her.

‘So I can’t ignore those girls now,’ he said.

Despite herself, she felt that flood of relief. ‘Do you mean . . .?’

‘I mean I’ll come to Bangladesh.’

For a second, she couldn’t speak. ‘Thank you, Ed.’

‘One condition,’ he said.

‘What?’ Anything.

He glanced round. ‘Sure?’

‘Yes.’ She didn’t have to think, agreed blindly.

He sat down on the other end of the bench, stared across the city.

‘This is the last time, Casey. Do you understand?’

She knew what he was asking.

‘After this, I don’t want to know anything more.’ He had turned towards her, his eyes hard. ‘I can’t know any more. It’s too much. It’s endless.’

So that no one can say, ‘I didn’t know.’