The German spy for the OSS, Frau Marianne Möllendorf in the movie, was a real person whom Erickson fell in love with. Her real name was Anne-Maria Freudenreich. The Swedish national archives in Stockholm have photographs and letters Erickson received from her.
When Erickson was meeting with the SS officer in his office, there is a menorah on the desk behind him.
The film cast includes two Oscar winners: William Holden and Hugh Griffith.
Publicity for this film made a point of saying that, unusually, each character was played by an actor of the same nationality. However, it seems likely that the part of "Collins", the ruthless spy chief, was written originally as an American for an American actor to portray - some of his dialogue seems more fitted to an American voice than to a Briton of the 1940s.