Chief took another sip of liqueur. ‘That had me stumped for longer. In the end I rang Bill Merriweather and asked him how he would have done it.’ Merriweather was our man at Porton Down, the Ministry of Defence’s chemical laboratory - back in ’56, he’d developed a nerve gas to use on Nasser. It would have worked, too. ‘He told me about a discovery someone on his team made a few years ago. Using a very strong tranquillizer called haloperidol, they found a way to stimulate what he referred to as “a temporary state of death”. The Russians have apparently been using the stuff on uncooperative prisoners for years, but if it’s administered correctly, it can induce catalepsy, which looks like death even to a trained eye. Bill thought there might be other drugs that could produce the same effect.’

‘I see,’ I said, although it all sounded a little fantastic. ‘But I don’t understand why you think this is the same woman Slavin is referring to. He doesn’t mention what name she was going under in 1945 . . .’ I picked up the folder again and found the place on the page. ‘“During and after the war, Irina Grigorieva, currently the assistant third secretary at the embassy here in Lagos, worked as a nurse in the British Zone of Germany. There she fell in love with a British officer, according to her the one true love of her life. She succeeded in recruiting this man into the NKVD . . .” It doesn’t say which hospital she worked at, and there must have been dozens in the Zone. Lagos Station’s photograph of her is also a little blurred - what makes you so sure she’s this Maleva?’

‘Instinct,’ he said. ‘Instinct and experience. I’ve spent half the afternoon examining her photograph - I can’t be one hundred per cent certain it’s her until I check its counterpart in Registry tomorrow morning, but I’m fairly close to that. It has to be her.’

He was looking at me expectantly. And that was when I saw what had been staring me in the face since he had answered the door. Why he’d called me out here tonight instead of leaving it until tomorrow morning. Why he was drinking more than usual. And why I had to act now.

‘You needn’t worry, sir,’ I said.

His broad face reddened immediately, and I knew I’d hit the mark. ‘Worry? What makes you think I should do that?’