He burst past me into the flat, without waiting to be asked. Then he started ranting. ‘Who put you up to it? You knew, didn’t you?’

‘Knew what?’

‘That these documents are fakes.’ He was red in the face, waving pieces of paper around in the air. ‘The ones purporting to show that the Russians had warned the British and Americans NOT to attack Dresden, because of the huge numbers of refugees sheltering near the railway station.’ Then he pointed his finger at my chest. I’d never seen this side of him, and I didn’t like it. ‘You knew, didn’t you?’

‘No, Arnie. I swear I didn’t.’

His face was virtually purple with rage. ‘I should have known it was too convenient. I meet up with someone I haven’t seen for more than forty years, and then suddenly they’re providing me with a lead to someone with secret documents that apparently made my thesis even stronger. Only they didn’t, did they?’

I slumped down. My head in my hands. ‘I honestly don’t know what you’re talking about.’

‘The man you introduced me to was a fake, and his documents were fake. It’s undermined my argument completely. I’ve been exposed by the university. I’m a complete laughing stock and my career is over.’

I racked my brains, trying to understand what’s gone wrong. Major Bahlow had assured me the documents would strengthen Arnie’s case. He claimed he had a personal interest in exposing the raids for what they were – just as I have.

‘I don’t know how this has happened, Arnie.’ I couldn’t admit to him that I agreed to work for the Stasi – that would be it. Our relationship – such as it is – would be over. ‘Is there anything I can do to put things right?’

I saw in his eyes then – eyes that were red raw, glistening with tears – that he was starting to believe me. That I was an innocent dupe in the Stasi’s game – I just couldn’t admit to him that it was a game I’d agreed to play, in return for a salary and specialist medical treatment.

‘I should just walk out of here and never see you again, Lotti. You realise you’ve ruined my life, don’t you? I stumble across the best information of my career, documents that virtually prove the Dresden firebombings were a war crime committed by Churchill and Bomber Harris. I didn’t even need these extra Russian documents.’

I wanted to tell him that he’s the historian, he should have checked his facts. Why didn’t he manage to find out for himself the Russian documents were fakes before he sent his research for peer review? But I knew that would just make him even more angry.