Topkapi (1964)

Beautiful thief Elizabeth Lipp (Melina Mercouri) and criminal genius Walter Harper (Maximilian Schell) put together a plan to steal an emerald-encrusted dagger from Istanbul's Topkapi Palace. As part of their crew, they hire small-time hustler Arthur Simon Simpson (Peter Ustinov) to act as their fall guy. When the Turkish secret police capture Simpson at the border, they persuade him to spy on his partners in crime, mistakenly believing that they're Communist agents plotting an assassination.