This movie is just wonderful! It centers on a group planning to steal a dagger covered in jewels from a Turkish museum. Maximilian Schell and Melina Mercouri form an amusing, attractive couple who put together a team to attempt this difficult heist. They also involve Peter Ustinov – a British con man making money by swindling visitors – as someone they intend to use. Things get interesting when he’s arrested and agrees to cooperate with the authorities. Robert Morley is excellent portraying the inventor of devices, and Gilles Ségal performs all the acrobatic stunts with a playful attitude. The writing hasn't aged well over the past 65 years—and many of the jokes seem rather obvious now—but the film has a fantastic aesthetic; it moves along quickly, feels sophisticated, and was quite unique for its time, featuring performers who work very effectively together. The music is familiar too – it immediately brings to mind dancers adorned with diamonds!

Source on TMDB