Hanne and Prince went from office to office, from department to department and from floor to floor looking for someone who’d help. But no one had heard of a Friedrich Steiner, nor of der Fluchtweg Falke or anything to do with kestrels or any other bird, or of Nazi escape lines for that matter.

After two days they were inclined to give up, and telephoned Gilbey, who told them he was confident they’d get Steiner sooner or later and felt they’d done their best so should return to England. When they managed to telephone Henry that evening, he sounded upset, worried that his father wouldn’t be coming home. They found the British liaison office in the building and arranged to get on a flight that was leaving in two days from RAF Wahn, just outside Cologne. The liaison officer – he’d introduced himself as Gibson – couldn’t have been more helpful. They told him about their mission and how they’d hit a dead end in Frankfurt and couldn’t find anyone to help them. He walked to the window, looking over the ruined landscape, then turned and spoke quietly.

‘Something you said just then…’

‘About the German – Steiner?’

‘No, about Nazi escape lines: what was it?’

‘We think Friedrich Steiner could have a possible connection to something called der Fluchtweg Falke – the Kestrel escape line.’

‘This could be a total coincidence, of course, but a couple of days ago, the Americans arrested an Englishman found in a bar with a briefcase containing nearly one thousand dollars and five hundred British pounds.’

‘That’s an awful lot of money,’ said Prince, ‘but I’m not sure I see the connection with what we’ve been asking about.’

‘His name is Charles Falmer and he’s a clerk with the British Army in Cologne. As far as I can tell from our chaps there, he’s not very important and wouldn’t be earning much – probably no more than a hundred pounds a year. The only explanation he offered was that he was in Frankfurt for a weekend off and this was his spending money, which as explanations go was about as unconvincing as you can get. You’ve seen this place – who’d come to a bombsite like this to relax? With that amount of money he could have bought half the city. They asked us to have a word with him. According to the Americans, he was caught in one of those bars where men go to meet other men, and at first I thought that was why he was so reluctant to tell us anything, but it still didn’t explain the money.

‘The Americans were minded to charge him with currency violation – they’re very anxious about their zone being flooded with dollars from the black market – and once I explained to him that this was a serious crime, he changed his tune and came up with a complicated story about how his uncle is an important art dealer in London and had given him the money to buy a painting from a man in Frankfurt. He said he was to meet the man in a small square called Elsa-Brändström-Platz, on Guiollettstrasse, where they have a flea market.’