When he arrived there a few minutes later, Bruno Bergmann was strapped to a rack on the wall, his arms and legs splayed and pulled hard so he formed an X shape. His arms supported his body weight and Lange knew it was only a matter of time before his shoulders dislocated. A spotlight had been trained on his face. He looked as terrified as Lange had hoped he would.

Lange pulled up a chair in front of him and lit a cigarette, a feeling of excitement and power sweeping through him. For as long as he could manage it, he said nothing. The only sound was that of Bergmann whimpering. After a while, he nodded to one of the two men standing on either side of him.

He was enormous, a former heavyweight boxer. He stepped forward and took up a classic southpaw stance: right foot slightly forward of the left, right hand up in a defensive position. Then he swayed forward and with his left hand punched Bergmann so hard in the stomach Lange was worried he might have killed him with one blow.

‘Leave him now,’ he instructed. ‘Bergmann, let me inform you of two things. We have your wife and children in custody. If you cooperate, their lives may be spared – certainly those of the children. We know you have a connection with Oberst Albert Kampmann. You can save your family…’ He paused here so that Bergmann could absorb the word ‘family’. Also, he didn’t look too good: his eyes were closing and blood trickled from his mouth. ‘You can save your family if you confess to everything.’

Which Bergmann did, telling Lange how he’d met Kampmann – whom he knew as Kurt – at a conference when he’d enquired about a series of technical issues. All along, he told Lange, he thought he was helping the Reich: that was his only motivation. By the time Kampmann had asked to meet his contact from Denmark, it was all too late. He bitterly regretted that—

‘Who is this contact from Denmark?’

Bergmann hesitated, but the boxer moved forward again.

‘Otto Knudsen, from Mortensen Machinery Parts, sir. We do an awful lot of work with them. They’re based in Copenhagen.’ Lange was smiling now, and Bergmann had obviously noticed and decided that this was a good sign. If he was cooperative, he was bound to be spared. ‘If it’s any help, sir, he stays at the Hotel Excelsior on Askanischer Platz. And on his last visit he was accompanied by another man from Copenhagen called Peter Rasmussen, whom I did not like one bit.’

Lange was delighted at how successful his interrogation had been. There was no question but that this would be looked on favourably by his superiors. He ordered Bergmann to be cut down and taken to one of the dungeons. He’d need to remain alive until the trial.