‘It doesn’t soften it. The luck and arbitrariness of life. And death.’

‘How about the bombers? Sacrificing themselves for their God.’

Patrick hesitated, unsure whether this was another of J’s tests. ‘I didn’t bother myself thinking about them,’ he replied.

‘Fair enough. But I’m asking you now.’

‘You’re putting me on a spot where I don’t want to be.’

‘Tough. Speak.’

‘They weren’t mad. Or sick. Or evil. Or any of the other tabloid epithets. They were sort of blinded. Blind-alley idealists.’

‘You can understand how they arrived at their destination.’

‘“Understand” may be putting it too strongly. I’ve felt anger. Destructive urges even, as a black boy at a British public school. But I could never graduate to the deed of killing.’

‘What about on the battlefield?’

‘Never been there.’

‘As a soldier in uniform,’ said J, ignoring his answer.

‘That’s different.’

‘Isn’t that what the bombers were? Soldiers in uniform fighting for Allah.’

Patrick frowned. ‘Where’s this leading?’

J ignored him. ‘Enough of 7/7. What about 9/11? Rather bigger deal. Deaths in the thousands.’

‘What the hell do you want me to say, J? That at least it had a bit of style about it?’

‘That’ll do,’ said J cheerfully. ‘You’ll get along with our friend splendidly.’

J jumped up from the sofa with surprising agility to remove two files from his bag, which, Patrick noted, was, for variety’s sake, a light tan rather than dreary brown. ‘I realise some of this may seem like an interrogation,’ he said mildly, ‘but the thing about working in intelligence is that it does pay to be intelligent. It’s all about the ability to get inside the other fellow’s head.’

From the first slender file, J fished out three photographs, cropped to show head and shoulders. Two were fuzzy, the third in perfect focus; together, they composed not just a face but the beginnings of an expression. ‘He’s called Kareem,’ said J. ‘Full name Kareem Abdullah bin-Jilani. Well-off Gulf State family, English public school educated, good degree.’ He bowed his head to peer over his glasses at Patrick. ‘Bit like you. But somewhere along the line, the similarities end.’ J retrieved the photographs and made a show of examining them. ‘A couple of days ago we invited Kareem for a chat.’

‘You invited him?’

‘If you’ll allow an elastic interpretation,’ he replied.

‘Kareem,’ repeated Sara, slowly shaking her head. ‘It seems impossible. And yet…’ She left the thought unfinished.

They’d stopped in the middle of Vauxhall Bridge on the Westminster side – to the right MI5’s cruise-liner frontage, to the left Millbank and Thames House beyond.

‘Yes,’ said Patrick, ‘Kareem. The man you sat next to in the restaurant. The man you already knew. Your turn to say something?’

‘No,’ she replied abruptly. ‘We’ll get to the end of your story first.’