For three days, he had stayed at the elegant Avenida Palace hotel, aware that he was being watched all the while by the German agents who crowded into its restaurant and bar. It was curious listening to – and mostly understanding – the stentorian babel of German voices. Even the laughter sounded Germanic. English and American voices were evident in other parts of the city, along with French, Spanish, and guttural sounds from Eastern Europe – tongues he could not identify. And Portuguese, too, of course. Their city, neutral territory in a Europe aflame, might have become occupied by half the world, seeking sanctuary, but it still belonged to them.

It was strangely unnerving to find himself in a country at peace.

Where Cambridge was grey, damp and rationed, Portugal was full of bright colours, delicious cooking smells and fine weather. And then a German diplomat named Anton Offenbach came to his hotel room, introduced himself and asked him about his plans to visit Berlin.

‘You know about me, then?’ Wilde instantly took the man to be a spy.

‘Of course, Herr Esser. You were expected – I saw your seaplane arrive at the Cabo Ruivo. How could we not know of you? Your visit is eagerly anticipated in Berlin. And on that subject, I have been asked to convey to my superiors exactly what it is that you are offering. While of great interest, the various messages that have been passed to us from your office in New York have not been altogether clear, I believe.’

‘I’m afraid that will have to wait until I’m there, Herr Offenbach. These are complex matters – not the sort of information to be transmitted down wires or by regular mail.’

‘Not even the diplomatic bag from our Lisbon embassy? I assure you it is quite secure.’

‘No, Herr Offenbach, not even that. And with all due respect, I don’t even know for sure who you are. You could be an English or American spy for all I know. You certainly speak remarkably good English, and I’m told this town is full of secret agents.’

Offenbach smiled reassuringly. ‘I studied modern languages at Oxford University, hence the English. Of course it did not harm my prospects of a position in the Auswärtiges Amt.’

Of course it didn’t. Junker class. Same story everywhere in the world – upper-middle-class scions fast-tracked into important and safe roles in foreign ministries. Same story at the State Department in Washington and the FO in London. Seamless rise to the top and a long way from the front line. But Wilde had no intention of letting him off the hook.

‘I only have your word for that.’

‘I understand entirely. But what of you, Herr Esser – are you a spy?’

‘Do I look like one?’

The man who called himself Offenbach laughed.

‘If you must know, you look like one of my old professors at University College, though rather more muscular in build. Appearances clearly mean nothing. So be it. Your flight to Berlin leaves in the morning. Nine sharp.’