Elizabeth Lipp (Melina Mercouri) visits Istanbul, where she sees a traveling fair featuring replicas of treasures from the TopkapÄ± Palace. Next she cases the TopkapÄ±, fascinated by the emerald-encrusted dagger of Sultan Mahmud I. Leaving Turkey, she recruits her ex-lover, Swiss master-criminal Walter Harper (Maximilian Schell), to plan a theft of the dagger. They engage Cedric Page (Robert Morley), master of all things mechanical; Giulio, "The Human Fly" (Gilles SÃ©gal), a mute acrobat; and the burly Hans (Jess Hahn), who will provide the muscle needed for the job.
Harper and Lipp then hire small-time hustler Arthur Simon Simpson (Peter Ustinov) to drive a car into Turkey to transport hidden explosives and firearms for use in the burglary. Turkish Customs search the car, find the firearms, and conclude that the gang are plotting an assassination. They then recruit Simpson to spy on Harper and Lipp. Page, picking up the car in Istanbul, is told a police ruse that only the "importer" Simpson is permitted to drive it in Turkey. While traveling with the gang, Simpson leaves notes for his police handlers, but most of his intelligence is worthless.
Hans' hands are injured in a scuffle with the drunken cook, Gerven (Akim Tamiroff), and Simpson is engaged as a substitute, prompting him to confess that the police are watching them. Harper arranges to give the police the slip. That evening, Harper, Simpson, and Giulio steal the dagger and leave a replica in its place. Unnoticed by the thieves, during the robbery a bird flies through the window they entered and is trapped inside the room when the window is closed.
The gang deliver the dagger to Joseph, proprietor of the traveling fair display, who will smuggle it out of the country. The gang members then go to police headquarters to "reveal" their discovery of weapons in the car. The inspector asks Simpson to vouch for Harper and Lipp's whereabouts that day. Simpson backs up their alibi; however, the inspector learns that the TopkapÄ± alarm was triggered by the trapped bird. Simpson's notes to the police provide a connection between the gang and Joseph's replicas of the TopkapÄ± treasures.
Ultimately, the gang is seen in a Turkish prison, where Lipp begins to tell them of her fascination with the Russian Imperial Crown Jewels in the Kremlin.
Whom does the gang deliver the dagger?
Joseph