‘Please stand, Dr Southwick,’ says the younger-looking man – speaking in English, but with a distinct German accent. I struggle to get to my feet, wincing from my bad leg. ‘I am Colonel Rainer Specht of the Ministry for State Security. And this is Gordon Breitmann – here on behalf of . . . of the British government, shall we say.’

‘A pleasure to finally meet you, Dr Southwick,’ says Breitmann, who – despite his German-sounding surname – speaks in a clipped Home Counties accent. ‘You’ve proved quite elusive these past few weeks – almost as though you didn’t want us to find you.’

Specht goes back to the door and opens it again. Two uniformed guards enter. They immediately begin to search the cell – pulling up the straw mattress and patting underneath it. One of them pulls out an odd-shaped object, wrapped in some sacking material. He unwraps it, taking care that he uses the material to grip it, presumably so as not to transfer any of his fingerprints. My stomach flutters – it’s a gun. How the fuck did that get there? Then I remember my first chance of a shower in the communal block after weeks in hiding, how I was so grateful for what I saw as a small act of kindness. It obviously wasn’t. It was simply the opportunity to plant the gun in my cell.

The guard hands it to the Stasi colonel.

‘What were you planning to do with this, Dr Southwick?’ he asks. ‘Aren’t you in enough trouble already?’

‘I-I-I’ve never seen that before.’ Immediately I realise that – although I’m innocent – I sound guilty and terrified.

Specht gestures with his eyes to the guards, indicating they should leave. Then he pulls over the cell’s stool – the only place to sit, other than the bed – and pushes me down onto it.

‘You’re in a spot of bother, I’m afraid, old chap,’ says Breitmann, towering over me. ‘We can only help you so far.’

‘Who’s we?’

‘I suppose you could say the Foreign Office, after a fashion. The point is, you’ve angered the British government by contravening the Official Secrets Act in propagating classified documents, and handing them to a foreign power.’

‘I did no such thing,’ I splutter.

‘Well, actually, you did. You made them available to the East German authorities via your research thesis, for which you were paid, I believe.’

‘Paid?’

‘You received a salary from Dresden University of Technology,’ continues Breitmann. ‘That salary was in turn paid for by the Ministry for State Security.’

I can’t help the gasp that comes out of my mouth. ‘Well, I never for a minute suspected that.’

The younger, German man, intervenes. ‘Your signature is on the agreement.’ He pulls a document from his briefcase and hands it to me. ‘Are you saying that’s not your signature.’