The Hour of 13 (1952)

Nicholas Revel (Peter Lawford) is a young man every dowager in London welcomes to her parties. He has taking ways, and the Calgurie Emerald is one of the things he takes. This daring theft brings unexpected complications, among them Jane Frensham (Dawn Addams), the daughter of the head of Scotland Yard, Sir Herbert Frensham (Sir Michael Hordern) and a maniacal killer loose in London. Revel sets a trap for the madman, with himself as bait, in a fog-shrouded stalk where one of them must die.