Elizabeth Lipp (Melina Mercouri) conspires with her former lover and teacher Walter Harper (Maximilian Schell) to steal a jewel-studded dagger from the palace in Istanbul. In order to accomplish this without getting caught, they use local amateurs to avoid being traced.
One of the locals is a Greek con man of British origins, Arthur Simpson (Peter Ustinov, in his Oscar winning role), who they hire to drive a car with hidden weapons across the border. The car is stopped, Simpson is arrested and forced to work for the Turkish government. They instruct him to get close tothe gang (who the government thinks is planning an assassination), and he passes on several notes, telling them what he has over heard.
The plan involves droping a "Human fly" from the roof of the palace, down through a window and over the jewels, to avoid sensors on the floor (Borrowed for Mission Impossible). Simpson is brought in on the plan after the original man hired to lower the human fly breaks his hands (eerily reminiscent of the newer Ocean's 11), and he stops helping the Turkish Secret Police.
All goes according to plan during the robbery, and they are able to steal the dagger and escape. Unfortunately, as they close the window to the jewel room, a little bird slips in and lands on the floor, setting off the alarm and alerting the guards. The entire band of thieves is captures and arrested.
The movie ends in a Turkish prison, with Elizabeth filling the gang in on a plan of hers to steal the Romanov jewels in the Kremlin, followed by a jaunty technicolor sign, saying "Here they go again!"
Thanks Paul B!