‘Too long,’ Julie responded. ‘Why do you ask?’

‘You seem very comfortable with each other, which I guess is important in a world where no one trusts anyone.’

Tess Winkelman hurtled towards the table long before the waiter could do the honours. Less statuesque than the photograph in her Foreign Office file suggested, and prettier too, if you could ignore her distinctly Roman profile, she wore a fawn linen jacket, crumpled by the heat, and sunglasses instead of a hairband, though the light had been fading for hours. Vivid blue eyes sparkled as she introduced herself, though her handshake was perfunctory. She slipped her bag from her shoulder and sat heavily next to Julie, as if she’d been too long on her feet.

The introductions complete, Tess ordered water at the precise moment Kate and Julie were served their cocktails. She didn’t bat an eyelid. ‘I hope you approve of the venue,’ she said. ‘I thought it was charmingly appropriate, under the circumstances, and anyway, I come here quite often. The food is excellent.’

They ordered off the tasting menu, which offered Circassian Chicken, Beef Stroganoff and Chicken Kievsky, and kept resolutely to small-talk – the daily life of a diplomat in this ancient city, which sounded enviable – until the main course had been served. Kate took the plunge first. ‘We’d be grateful if you could start at the very beginning. Leave out no detail, however apparently insignificant. We never know what’s going to come in useful.’

Tess Winkelman toyed with her food for a moment. ‘I suppose what strikes me when I think about it is the change in her demeanour. Either something along the lines she suggests did take place, or she’s a highly competent actor.’

‘Not unknown in the intelligence community,’ Kate said.

‘I’m sure,’ Tess agreed, waving her fork. ‘Look, I knew who she was, of course. As I’m sure you’re aware, part of the briefing prior to taking up an appointment like mine involves instruction on known agents operating undercover for foreign intelligence networks.’

Kate wondered how it was that the Foreign Office appeared to have suspicions about Natasha Demidova that had not found their way into the SIS files.

Tess helped herself to a mouthful of chicken, chewed it slowly and swallowed. ‘I first encountered her at the Russian ambassador’s Christmas reception the year before last. But we were only introduced very briefly. Shortly after that, I saw her at the tennis club I’d joined over in Bebek.’

‘Does she play there regularly?’ Kate asked.

‘Every morning. And she’s good. I mean, really good. Might-once-have-considered-becoming-professional kind of excellent. I can hit a ball myself – I once played Junior Wimbledon – but she’s at a whole different level. She usually played on the next-door court, mixed doubles, with a woman from Slovak intelligence called Nela and two men, who I think were also from the Russian Embassy.’

‘Did you speak to her?’

‘No, but … I don’t know how to put this without sounding rather too pleased with myself, but I sensed a mutual recognition of ability, if you see what I mean. After that, we’d nod at each other now and then around the club.’