Good Luck, Charlie (1962)

Charlie Pattison, a wealthy American, lands at Athens airport, where he has just received an emergency phone call from his friend Maurice. The two men met in prison camps and have vowed to track down a certain Nazi doctor, Hermann Geiss, a connoisseur of masterpieces who is guilty of criminal experiments on prisoners. But Maurice doesn't show up. As soon as he arrives, Charlie investigates his friend's disappearance. He ends up meeting a painting dealer, Cardin, whose client Geiss is said to have been.