Mum's the Word(1960)

Martin is a nurse in a private clinic in Paris. The victim of a serious concussion, an unidentified casualty, arrives in the emergency room one night. He is operated on immediately. When he wakes up, half-unconscious, he tells Martin a confused story about stealing jewels from a maharajah visiting Marseille... before falling into total amnesia. Real and fake policemen interrogate Martin, gangsters kidnap him to get him to reveal precious information, but... the nurse keeps his mouth shut!