He liked that.

Now that he was aboard the flight, he knew he would not have long to wait until he put Mrs Kemp’s tuition to the test.

The cognac arrived. Wilde inhaled its heady fumes, took a sip then knocked the rest back in one. He held the glass out for another, but then thought better of it and put his hand over the top. He would need a clear head. Death only required a single misstep.

His journey thus far had been circuitous. In America, he had been told, the real Tomas Esser had not been entirely co-operative at first. It wasn’t true that he was a Nazi sympathiser, but nor was he inclined to do anything to harm Germany or his company’s potential for dealing with the regime.

In the end, under pressure from Roosevelt, via his close aide Bill Donovan, he had acceded to the COI’s entreaties and handed over his passport. It was clear to the few people in the know about this mission that it would be better to use genuine papers rather than forgeries. The fact that Esser bore a passing resemblance to Wilde made this feasible.

One of the obvious differences was that Esser wore spectacles in his passport photograph, while Wilde wore them only for reading. In New York, a pair had been made up in Esser’s frames with the lenses Wilde used in his research studies. He would wear them halfway down his nose so that he could peer over the top. Esser also had a thin moustache, so Wilde had had to grow one. Put side by side, the real Tomas Esser and the fake one would be easy to distinguish, but against a battered passport photo, Wilde was confident he could pass muster.

The real Tomas Esser, meanwhile, had been taken to a safe house in Vermont – again, unwillingly. There were too many Nazi spies in America for him to be allowed to roam free. All his secretary would be able to say was that her boss had left the office for a few days; and no, she was unable to say where he had gone or when he’d be back.

While the hapless Esser enjoyed an enforced furlough of fishing and long walks in New England, the copy of his spectacles, along with his actual passport, had been shipped to Horta in the Azores aboard the Clipper flying boat service. Wilde, meanwhile, had been taken to the islands by a fast Royal Navy corvette. It would have been preferable, perhaps, for him to travel to America and start his journey as Tomas Esser there, but time was of the essence – and picking the flight up in the Azores instead had been a risk worth taking. The chances that Nazi agents were monitoring the passenger lists in Port Washington, New York, were surely minimal.

From the Azores, Wilde and his new accoutrements – glasses, papers, American clothes, a battered old suitcase belonging to Esser, toiletries from Saks Fifth Avenue and a new, shorter haircut – had joined the Pan Am craft for the last leg of the journey to the seaplane base on the Tagus river, close to the Portuguese capital, Lisbon.