‘So someone knew what he was up to in Geneva and tipped off the Russians?’ Simpson said. She was looking directly at Kate.

‘It looks that way, yes.’

‘And it could not have been your husband?’

‘That’s correct, ma’am.’

‘To be honest, I’m surprised these questions were not asked before,’ Suzy said. They all turned towards her. Even Simpson was frowning at what felt like a gratuitous twist of the knife. ‘I didn’t mean . . .’ Now it was her turn to redden.

‘Who knew enough of what Rav was doing to tip off the Russians?’ Simpson asked.

‘Chiefly me,’ Kate said.

‘I knew,’ Sir Alan added. ‘So did Ian and Julie.’

‘Just the four of you?’

‘I would say so.’

Kate stared at the floor. My God, she wished Operation Sigma had never darkened her door. Nothing good had come of it, nothing at all. Kate wondered if Sir Alan would mention that the Russians seemed to have been tipped off about Estonia as well, but he must have decided that discretion was the better part of valour and she was not about to argue with him.

‘Well, we can’t pretend this is anything but uncomfortable,’ Simpson said.

‘My colleagues in Five will certainly want to know why these questions weren’t asked before,’ Suzy said.

Sir Alan looked at her. ‘You are a very clever and ambitious woman, Miss Spencer, but you are in danger of overplaying your hand here, if I may say so.’ Sir Alan’s voice was at its most acid. ‘We did not involve our colleagues at Five because we wanted to protect our operational integrity and the security of its ultimate source, Lena Sabic, the au pair we recruited to bug Igor’s super-yacht. Once the operation was complete, we had no reason to believe anyone other than Stuart was Viper.’ He glanced at Meg Simpson, before turning to Suzy and leaning forward to emphasize his point. ‘Your logic makes several fairly enormous leaps. We have never determined who killed Rav or why. Perhaps it was the Russians, but it may have been someone else entirely, for motives we have not yet uncovered.’

‘The file makes it clear you thought it was the Russians,’ Suzy said tartly. She did not look as if she was enjoying her ticking off.

‘Supposition and fact are two entirely different things. We don’t know what Rav was up to. He was off the grid and not following orders from anyone here. Perhaps he met someone we are not aware of, or made a call using a landline. Or it may just be that the Russians had the lawyer or his assistant under surveillance.’

‘I acknowledge all those possibilities, but I still think we should—’

‘Close this down now.’ Sir Alan smiled at her again. ‘We have bigger fish to fry. We are potentially being offered evidence that our prime minister is a traitor, who seeks to undermine our response to Russian aggression. Nothing is more serious than that, and we cannot allow anyone to stand in the way of pursuing this matter to its logical conclusion in Berlin over the next few days.’