The film is set in the mythical country of "Vosnia", which, according to director Sidney Gilliat, was meant to suggest either Spain (to left-wingers) or what was then Yugoslavia (to right-wingers). A special "Vosnian" language was devised for the film by Georgina Shield, a teacher at the London School of Languages, and several of the actors took lessons in how to speak it over a period of several days, as it is extensively heard in the film.
Carl Jaffe appears as 2 separate characters: Prada the government envoy who meets Marlowe at his club, and later as the briefly-glimpsed tug-boat skipper.
Glynis Johns is the film's leading lady and is second-billed; however, she does not appear in the film at all for the first forty-five minutes, nearly half-way through.
A brief segment of this movie was recreated on NBC Radio's "The Big Show" starring Talullah Bankhead. Because this segment did not give any idea of how the movie ended, Ms Bankhead offered the cost of a movie ticket to find out the ending.
The film has the same basic plot as Crisis (1950), both being filmed at the same time without any knowledge of the other. In an interview on the 2020 Blu-Ray release, the film's publicity director Forbes Taylor speculates that the plot had been floating around in Hollywood for years and both studios had accidentally picked it up at the same time.