Suzy looked as if she might object, but thought better of it after catching sight of the expression on Sir Alan’s face. Ice radiated more warmth. ‘Talk me through the operation,’ he said. He was still addressing Kate, as if the others were not there.

Kate shook her head. ‘I’m still confused by it. Danny and his team were convinced I was clean by the time I arrived in Alexanderplatz. I don’t know how Mikhail got a burner phone into my pocket. And I have no idea how they managed to ambush me at that point in Friedrichstrasse.’

‘Did you raise it with Mikhail?’

‘I asked him whether Stuart was Viper.’

‘What was his answer?’

‘He said Stuart was definitely Viper, but he seemed less sure about the possibility of another mole. I suggested that a second source was working for the GRU.’

Sir Alan fixed each of them with a steady gaze in turn, his pale blue eyes tinged with a melancholy Kate had never witnessed before. ‘Who knew about the meeting in Alexanderplatz?’

Suzy stood up, as if this had been her cue. ‘The same group. You, Kate, Julie, Danny.’

‘And you,’ Kate told Suzy.

‘And me, yes, though I can be ruled out since this mole, if he or she does exist, was part of the original Operation Sigma.’

‘That’s merely your conjecture,’ Kate said. Suzy flushed. For a woman so tactless, she appeared to have a strange aversion to confrontation.

‘What about Ian?’ Julie asked.

‘I informed him,’ Sir Alan said. Kate tried to conceal her surprise. Ian had not bothered to ask her the details of the operation in Berlin – which, now she came to reflect on it, was odd in itself – and it would have been all too easy for Sir Alan to keep them from him. If there was a potential leak, then the need-to-know principle ought to have been paramount.

The thought came to her unbidden that Sir Alan’s actions could be interpreted as a deliberate attempt to widen the circle of knowledge.

‘What about the foreign secretary?’ Julie asked.

Sir Alan shook his head. ‘She didn’t know the time or the place of the meeting.’

‘She was aware of the time,’ Kate said quietly. ‘And she knew it was in Berlin.’

‘All right,’ Sir Alan said, moving towards the door. ‘We’re going around in circles. It’s quite possible they’ve been monitoring Mikhail. Kate and I will pick this up with the foreign secretary in the morning. Suzy, I want you and Julie to start preparing the ground in Tbilisi. Work on the assumption that we’ll get approval for the extraction and permission to hire some kind of private jet. And whatever security detail you think we might need, double it.’

‘Should we inform the Georgians?’ Suzy asked.

Sir Alan looked incredulous. ‘Of course not,’ he said, and Kate could see Suzy privately cursing her inexperience.