Love in the Afternoon (1957)

In Paris, private detective Claude Chavasse, known for uncovering infidelities, is hired to follow a wife suspected of an affair with wealthy American playboy Frank Flannagan. When the jealous husband threatens to shoot Flannagan, Claude's daughter, Ariane, overhears and rushes to warn him. Intrigued by the mysterious young woman, Frank begins a whirlwind romance with Ariane, leading to jealousy and a dramatic decision.