The Secret of Stamboul (1936)

James Mason is "Larry" - a British agent sent on a top secret mission to Turkey. He is soon amidst a conspiracy to dethrone the Sultan and he hasn't a clue whom he can trust. Valerie Hobson - "Tania", an aristocratic refugee from the Russian revolution; Frank Vosper - the superbly seedy "Kazdim" and/or Kay Walsh ("Diana") - take your pick. There are a few (fairly obvious) twists in the story, and the plot has little by the way of jeopardy, but the writing (adapted from the Wheatley novel "The Eunuch of Stamboul") is decent enough and Mason is on good form as the dapper and intrepid spy who has shades of the swashbuckler about him. It's all a bit formulaic, but enjoyable nonetheless.