The old Hotel Prinz Albrecht Strasse was an unremarkable four-storey building of arched windows and mock Corinthian pillars, with two long, dictator-sized balconies on the first floor, surmounted by an enormous ornate clock. Its seventy rooms meant that it had never been in the same league as the big hotels like the Bristol or the Adlon, which was probably how it came to be taken over by the SS. Now called SS-Haus, and situated next door to Gestapo headquarters at number eight, it was also headquarters to Heinrich Himmler in his capacity as Reichsführer-SS.

In the Personnel Records Department on the second floor, I showed them my warrant and explained my mission.

‘I’m required by the SD to obtain a security clearance for a member of the SS in order that he may be considered for promotion to General Heydrich’s personal staff.’

The SS corporal on duty stiffened at the mention of Heydrich’s name.

‘How can I help?’ he said eagerly.

‘I require to see the man’s file. His name is Otto Rahn.’

The corporal asked me to wait, and then went into the next room where he searched for the appropriate filing-cabinet.

‘Here you are,’ he said, returning after a few minutes with the file. ‘I’m afraid that I’ll have to ask you to examine it here. A file may be removed from this office only with the written approval of the Reichsführer himself.’

‘Naturally I knew that,’ I said coldly. ‘But I’m sure I’ll just need to take a quick look at it. This is only a formal security check.’ I stepped away and stood at a lectern on the far side of the office, where I opened the file to examine its contents. It made interesting reading.

SS Unterscharfiihrer Otto Rahn; born 18 February 1904 at Michelstadt in Odenwald; studied philology at the University of Heidelberg, graduating in 1928; joined SS, March 1936; promoted SS, Unterscharführer, April 1936; posted SS-Deaths Head Division ‘Oberbayern’ Dachau Concentration Camp, September 1937; seconded to Race and Resettlement Office, December 1938; public speaker and author of Crusade Against the Grail (1933) amd Lucifer’s Servants (1937).

There followed several pages of medical notes and character assessments, and these included an evaluation from one SS-Gruppenfuhrer Theodor Eicke which described Rahn as ‘diligent, although given to some eccentricities’. By my reckoning that could have covered just about anything, from murder to the length of his hair.

I returned Rahn’s file to the desk corporal and made my way out of the building. Otto Rahn.