Prince moved in front of Otto, grabbing him by the shoulders. ‘Pull yourself together! There’s nothing we can do about the others. We need to act normally: return to the hotel, go to the factory in Spandau in the morning and then fly back to Copenhagen in the evening as planned. If we do anything unusual, we’ll just be drawing attention to ourselves.’

For the second night in a row, Prince hardly slept. This time it wasn’t the heat or the noise but the events of that evening that kept him awake.

The meeting with Kurt had been very productive: he’d answered the questions London had passed on to him and the information about Peenemünde felt like gold dust. If that didn’t satisfy London, then nothing would. Prince thought he could be home within a week, two at the most, and would finally see Henry.

But then the drama: the woman in the hat. He’d been right in assuming she was watching him, but it wasn’t for the Gestapo. She must be on the same side as him, but who did she work for? Was she a companion of Kurt’s, there to watch his back?

And then he wondered about Kurt: had he been followed to the restaurant? And how come they’d been able to escape with relative ease? Could it all be a web of deceit they’d been drawn into?

He knew there was little they could do other than stick to their routine for the day, which meant being at the hotel entrance at a quarter to eight for the car to take them to Spandau Locomotive Engineering.

Otto hardly said a word in the car. He’d been more or less silent since they’d met in reception that morning. He’d clearly not slept, and the smell of vomit was still on his breath. The tension in the car mounted as they passed through Charlottenburg. Neither of them had any idea what had happened to Bruno after they’d spotted him in Kommandantenstrasse, just before they were stopped by the Gestapo. The only straw they could cling to was that they both agreed the shooting appeared to have been further away, closer to the restaurant.

To their relief, as the car pulled through the factory gates, Bruno was standing on the steps of the office block, peering anxiously out to the car park. The friendly engineer was in a terrible state. He looked pale and gaunt; his red-rimmed eyes had a haunted look to them.

‘Come this way,’ was all he said before leading them down a long corridor into a noisy basement workshop, the smell of grease and diesel fumes almost overpowering.