Sir Alfred Hitchcock convinced Sir John Gielgud to play the lead by describing the hero as a modern-day Hamlet. Gielgud, however, ended up hating that his character was an enigma.
Based on W. Somerset Maugham's "Ashenden" spy stories ("The Traitor" and "The Hairless Mexican") and a play by Campbell Dixon.
Sir John Gielgud filmed this during the day while appearing on-stage in "Romeo and Juliet" opposite Dame Edith Evans, Dame Peggy Ashcroft and Sir Laurence Olivier in the evening.
Sir Alfred Hitchcock reflected (regarding Sir John Gielgud's lack of heroics): "You can't root for a hero who doesn't want to be one."