Irma La Douce, a successful Parisian poule who plies her trade on a narrow street off Les Halles, gives all of her earnings to Hippolyte, her mec . Onto the scene comes a young, naive, and honest policeman, Nestor Patou, who, shocked by the open vice, conducts an unauthorized raid and arrests all the streetwalkers who frequent the bistro Chez Moustache. Unfortunately, Nestor's superior, Inspector Lefevre, is among the men arrested, and Nestor is fired from the force. He takes up with Irma, and, after a fight with Hippolyte, becomes her new mec . He soon falls in love with Irma and becomes jealous of her customers. With the help of Moustache, Nestor poses as a wealthy Englishman, Lord X, who claims he wants only a companion since the war has rendered him "useless." He agrees to pay Irma a huge sum for one visit a week, but in order to pay he is forced to work in the marketplace. Every morning, Nestor returns to Irma too tired to make love, and she begins to suspect that he has another lover. Irma then asks Lord X to take her to England and manages to seduce the supposedly impotent Britisher. As Irma packs to leave, Nestor decides to "murder" Lord X and dump all traces of him into the Seine. He is followed by Hippolyte, who, hearing a splash and seeing Lord X's clothes floating on the water, turns Nestor in as a murderer. Nestor is sent to prison, but when he hears that Irma is pregnant he escapes and reemerges from the Seine as Lord X, thus vindicating himself. At the church where Nestor and Irma are married, Irma collapses and has her baby. All ends well, however, when Nestor is reinstated by Inspector Lefevre; and Irma is able to contemplate a happier future.
