Set in WW I, Gielgud plays a novelist/soldier who gets a new identity and becomes a British spy. He joins up with a professional assassin (Peter Lorre) and they venture to Switzerland in search of a German operative.

The one person who might have knowledge of the spy's identity turns up strangled and some guesswork lead them to a "suspect."

When they assassinate the wrong man, Gielgud has second thoughts about his new occupation until the real spy reveals himself.

Hitch convinced 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 and felt Hitch made the villain more charming than the hero.

Hitch reflected (regarding Gielgud's lack of heroics): "You can't root for a hero who doesn't want to be one."

Based on Maugham's "Ashenden" spy stories ("The Traitor" and "The Hairless Mexican") and a play by Campbell Dixon.