Istanbul, winter 1938. A corpse washes onto the beach, which the police identify as famous, wanted criminal Dimitris Makropolous. The death intrigues visiting mystery writer Cornelius Leyden, who unravels the lethal web of deceit, blackmail and murder behind The Mask of Dimitrios. Following the trail left by Dimitrios (Zachary Scott), Leyden (Peter Lorre) boards the famous Orient Express for Sofia, where he meets jovial Mr. Peters (Sydney Greenstreet), gradually realizes that the Dimitrios may not be dead ... and uncovers Mr. Peters' dangerous scheme to use him to blackmail a murderer.