There are two types of police checks on trains: bad and not so bad. The not so bad are the Bahnschutzpolizei – that’s the railway police. Here are some pictures of their uniforms, please have a good look. And then there’s the bad: the Gestapo.

There were two men working the carriage, and with their distinctive gunmetal-grey tunic with black trim and black trousers, he could tell they were both Bahnschutzpolizei.

‘Tickets! Identity cards!’

The passengers either side of him took their time, and by the time the Bahnschutzpolizei officer had finished with the old woman, he looked irritated. Further down the carriage, his colleague called out to him: ‘Hurry up, Franz, we’ll be in Stralsund soon.’

‘By the time this lot find their tickets, we’ll be on the return leg to Rostock. You, come on!’

Prince handed over his ticket and identity card. The Bahnschutzpolizei officer studied the ticket carefully. ‘Where are you going to?’

‘Greifswald.’

Then the identity card: the familiar and dreaded head movement, looking down at the photo on the card and up again at his face. Up and down. Repeat.

‘Name?’

‘Ulrich Leuschner.’

‘Speak up, man!’

‘Ulrich Leuschner.’

‘The purpose of your journey?’

He was saved by two people. First by Frau Henlein, who told the Bahnschutzpolizei officer the man was unwell and he should leave him alone, and then by the officer’s colleague shouting again: they really needed to get a move on. He handed the papers back to Prince and carried on.

‘Perhaps you’d like some more schnapps?’ asked Frau Henlein. ‘You really don’t look so good.’

‘So those are my instructions – seriously? I arrive at Greifswald and do nothing?’

‘You’ve not been listening Peter: I didn’t say do nothing, did I? You leave the train…’

‘Obviously.’

They were in the apartment in Copenhagen and Hanne was giving him his final briefing. She’d received instructions from London.

‘…then you walk out of the station. Blackbird will greet you soon after that. They will say, “You look so well after such a long journey,” and your response is… go on, Peter, your response?’

‘I’m to say, “But I could do with a good meal and a proper sleep.”’

‘Correct.’

‘Which is all well and good, but what is my fallback story?’

‘What do you mean?’

‘It’s supposed to be rule number one when in enemy territory: know where you’re going and have a story to tell in case you’re stopped. If I’m stopped before I leave the station, what am I to say? With this identity I won’t last a minute.’

She looked at him as if she knew he was right. ‘Hopefully it won’t come to that.’