James Mason, as Diello, delivers an excellent performance in this compelling WWII spy narrative. He plays the outwardly helpful valet for the British Ambassador stationed in Turkey. However, he also has a side business involving confidential information, and when he joins forces with the newly impoverished Polish “Countess Anna” (Danielle Darrieux) to clean up some illegally obtained money, he sets his clever scheme into motion: to gather enough funds from the Nazis so that he can retire as a wealthy individual in South America. As British authorities become suspicious, Michael Rennie ("Travers") is sent over from London to look into things. This creates stress for our deceitful character, and when his accomplice runs off with all of the money, he needs to act quickly to stay alive... The film opens with a question raised in Parliament regarding whether a newspaper article describing this unbelievable scheme is genuine, suggesting that there's some basis in reality. Furthermore, the fact that the Nazis were so eager for the information but not confident enough in their source to actually utilize it adds another layer of intensity to the story. Mason brings considerable flair to his likable, albeit completely dishonest, character and the rest of the well-assembled cast maintain a good pace throughout. Joseph Mankiewicz filmed the production in Istanbul, which contributes to the realism of this genuinely absorbing drama with an appropriate ending. It's a worthwhile film!

Source on TMDB