The reality, however, was very different: he was flying in a Nazi-controlled airplane over fascist Spain towards occupied France, and then into the very heart of Hitler’s Reich. His preparation for the mission had been crunched into ten exhausting days. Ten days of getting the cover story right, of getting used to the name Esser, of ensuring there were no British labels or laundry marks on any item of clothing, that his United States papers were in order. And what seemed like a hundred other tiny details which could catch him out.

Ten days in which he had grown a moustache and become accustomed to wearing spectacles all the time.

Cashbone didn’t have the expertise to train him in tradecraft, so Eaton had brought in Britain’s SOE to help. And if the training had been short, it had been correspondingly intensive. He’d felt as if he was on a dizzying roller coaster.

Going down to London after that lunch with Lydia, he had fondly imagined he would be taking control of an office, helping to build up the new COI organisation as Roosevelt and Bill Donovan desired. It had not occurred to him that he would be thrust straight into the field, on a mission involving extreme danger.

When he had expressed his reservations, Cashbone had been apologetic.

‘Something’s come up, I’m afraid. We have no one else to call on. The package is vital – it’s a mission that could have a profound bearing on the course of the war. For the present I can’t tell you any more than that.’

What could he do? He had always believed that one had to fight for peace and freedom, however contradictory that sounded. He had missed the first war; he couldn’t miss this one – and so he had said yes, without having any real idea of what he was letting himself in for. And then, for ten days solid, from before breakfast until late at night, he had worked on transforming himself into Tomas Esser, American businessman, opportunist and Nazi sympathiser.

From London, he had been driven back northwards to a safe house not far from Cambridge, where he had remained under the tutelage of a stern, matronly woman named Rosamund Kemp, who was employed by the SOE to teach agents the German language and German customs. She was in her forties, he guessed, tidy, with a keen, clever eye.

They had talked German all day every day; she had prepared German food for each meal. And she had called him by his new name. In the beginning he had found her rather forbidding, but he had quickly grown to respect and even like her.

‘I’m not trying to make you seem German, Herr Esser. That would be impossible. But I want you to be at ease among Germans, so that you get the drift of what they are saying, especially when they think you won’t.’

When he left she did not wish him good luck. She merely said, ‘Hopefully, if all goes to plan, I will see you again in a week or two.’