‘Fuck you, Dark!’ spat Montcrieff, the first time I had seen him angry. ‘This doesn’t change that you’re a traitor. Confess now and . . .’

‘And what? You won’t arrange my hanging at Wembley? Something tells me the PM might not be too keen to sign the chit for that whatever I say, and even if it were signed by the real Foreign Secretary.’ I turned the screw. ‘Perhaps he’d be more interested in hearing how you planned to kill him. I bet you all loved it when Henry proposed the idea - it was Henry’s idea, wasn’t it? Kill Wilson, then pin the blame on Moscow and claim he had double-crossed his masters at the KGB. Masterful. Did he tell you an actual KGB agent would do the job, though?’ They didn’t respond. ‘How do you think he got her to do that? Did it not occur to you that his more-fascist-than-thou act might have been just that - an act - and that he was, in fact, leading you straight into a position in which the KGB could send a sniper to assassinate our prime minister?’

I let it sink in for a moment. Osborne rallied from the shock of me discovering their little subterfuge and waved the one-time pad at me. ‘This was found in your pockets when we searched you . . .’

‘And I took it from Henry’s pockets moments after I discovered he was Radnya and shot him,’ I said. ‘Radnya means “related” in Russian, and just as you were all delighted Henry had access to the Queen - who you would need to form a government - so were the KGB. What could be more precious than a double agent with blood ties to the throne?’ Their faces were turning white, so I closed in for the kill. ‘I suggest you send a team to Henry’s house and search the basement. Once you’ve found his transmitter, perhaps we can stop this charade and get down to the serious business of trying to assess just how much the bastard has compromised over the last twenty-five years.’

He was wearing a green tweed coat and a polka-dot bow tie. It had taken me four and a half hours to get to the meeting, and he’d turned up in an outfit a child could describe.

I wasn’t in the best of moods. I’d spent most of the day with a team from Five, searching every inch of Pritchard’s enormous flat in Belgravia. He’d made me sweat - for several hours I had seriously wondered if I might still be looking at the rope. In the end, it hadn’t been in the basement, or the attic, or under the floorboards, but in a compartment concealed in one of the bookshelves.

‘I want out,’ I said to Sasha. ‘I mean it.’ But it sounded weak, even to my ears.