* Jack Hawkins as Major Geoffrey "Geoff" Craddock, the British agent who becomes a double agent.
* Christine Carere as Countess Irina Petrova, a Russian spy who is Geoffrey's love interest.
* George Sanders as Major Von Richter, the German spymaster who suspects Geoffrey is a double agent.
* Frederick Valk as Colonel Erich von Liebenheim, a German officer who is suspicious of Geoffrey.
* Victor Maddern as Major Hans Mueller, a German officer who assists Geoffrey in his double agent mission.
* Irene Handl as Mrs. Poppy, a British intelligence agent who assists Geoffrey.
The film also featured supporting roles from actors such as:
* David Lodge
* Michael Ripper
* Peter Arne
* Donald Pleasence
* John Laurie