He was obviously confused now. But not half as disoriented as Kate was. Even as he spoke, her mind was spinning. If Stuart hadn’t told Moscow about Operation Sigma, who the hell had?

‘To be completely honest with you,’ he went on, ‘I sometimes wondered why they wanted to recruit me at all.’

She looked up at him again. ‘Why do you say that?’

‘When they cornered me – blackmailed me – it all seemed incredibly urgent and elemental. They were brutal. They said they’d show you the video of Imogen and me and destroy our love and marriage. I absolutely believed them. They seemed ruthless, determined. But almost as soon as they’d got what they wanted, it was as if their interest waned. I mean, we’d meet up – about once a month, on average, I suppose – but even then they’d quite regularly postpone one or other rendezvous. Every time I was so relieved and started to convince myself they’d lost interest.

‘And even when we did meet, they didn’t seem that interested in what I had to say. It was like going to lunch with a benevolent but distant relation, who was trying to feign interest in everything you do.’

Kate shook her head. ‘I don’t understand.’

‘It was almost as if the purpose of recruiting me was to tick a box, or meet a target. As I said, we talked about politics and Imogen, who was up and who was down. I discussed policy in some of the areas I was working on, but they weren’t at all interested in that. They asked about you or the Service only rarely and when I said I didn’t know anything, they didn’t pressure me to try to find out more. I didn’t tell them anything they couldn’t otherwise have picked up from watching the news.’

Kate was looking out of the window. A lorry had pulled up and an enormously fat driver stepped down and waddled towards the diner. She was pretty sure now that they were not being tailed, but she couldn’t make sense of why not. Did they intend to pick her up closer to the border? Perhaps they had a tracking device on Stuart’s car.

‘Did I say the wrong thing?’ he asked.

‘In what way?’

‘For a shot at redemption.’

‘It isn’t about that,’ she said, though in a way it was: a test of whether she thought he was capable of telling her the truth. ‘What you say is . . . surprising.’

‘Why?’

‘Their disinterest.’

‘I know. Sometimes I think it would have been easier if I had been passing vital state secrets. At least that would have felt important. They ruined my – our – life for nothing.’