Hanne didn’t reply. Her head was bowed.

‘I say, are you all right, darling?’

When she looked up, her eyes were filled with tears. ‘I knew some of those agents.’

‘Really – in Denmark?’

‘No, no – in Ravensbrück. Three women, British agents, were executed there. I remember their names: Violette Szabo, Denise Bloch and Lilian Rolfe. They were extraordinarily brave. One of them managed to talk to another prisoner and told her they worked for the British and that they’d been dropped into France by parachute.’ Tears streaked down her cheeks and Prince noticed that Tom Gilbey had placed a knuckle between his teeth in an effort to control his own emotions.

‘Fritz Suhren, the camp commandant, supervised their executions himself.’ She pronounced the name through gritted teeth. ‘If you ever catch him, I shall be a witness.’

Gilbey nodded, then continued. ‘One agent we flew over was a woman called Christine Butler. She was sent to France in December 1943 to organise the resistance in the Dijon area. Her group was betrayed and most of them were arrested. As far as we can ascertain, she was interrogated by a young Gestapo officer from Paris, who tortured her and – I’m sorry to have to say this, Hanne – raped her so badly she had to be transferred to the infirmary at Dijon prison.

‘He then turned up there and had her carried on a stretcher to the pavement outside the prison, where he shot her dead.’

Gilbey paused and sipped his tea.

‘We have a good physical description of the chap, which I’ll let you have, but what we don’t have is his name: he was apparently only known by his nickname – das Frettchen.’

‘The Ferret.’

‘Indeed: a nasty, mean little animal, a close relation of the weasel and the polecat – we had no end of trouble with weasels on my in-laws’ estate. My father-in-law took it personally, but then he takes everything personally. Anyway, we understand that after Christine Butler’s murder, the Ferret was transferred to Amsterdam, where he was involved in the death of an SOE agent and a young woman who ran the resistance group there. We don’t know what happened to him after that: he was transferred elsewhere, but we lost track of him. The man responsible for finding him is an old school chum of mine, Charles Lean… Did you say something, Prince?’

‘No, sir, it just seems that you went to school with an awful lot of people.’

‘It’s a large school, Prince. Charles ran agents for one of the SOE’s French sections and was the man who recruited Christine Butler. As the first officer to lose an agent to the Ferret, he has overall responsibility for bringing him to justice – that’s the way it works in the SOE. He put the Ferret’s details on a watch list, and lo and behold, a couple of weeks ago the American military police in Munich contacted him to say the man was in the city.