You'd Be Surprised (1926)

During a party given by a district attorney (Edward Martindel), a valuable diamond goes missing. The attorney turns the lights off so the thief can return the jewel anonymously, but when they come back on, he's been stabbed to death. The guests soon discover the man's ward (Dorothy Sebastian) in a large clock, clutching the stolen stone. Insisting that she has no idea who pushed her into hiding, the girl remains a suspect -- until the lights go out again.