Ariane Chavasse, the daughter of a private detective, becomes intrigued with one of her father's cases involving notorious American playboy Frank Flannagan. They meet secretly in the afternoons and soon Frank finds himself falling in love. Jealous of the other lovers Ariane pretends to have, Frank hires her own father to find out more about her. Detective Chavasse tells Frank the truth and asks him to leave Paris for Ariane's sake. But when Ariane sees him off at the train station, they leave together.