Set in Paris at the start of the Roaring Twenties, La Garçonne follows Louise Kerlac who witnesses the murder of a family friend. A career forbidden to women at the time, Louise is convinced that joining the police will be her best hiding place while also providing the means to investigate the murder. She therefore assumes the identity of her twin brother Antoine and becomes a police detective, as a man. During this time, the disappearance of several young models posing for the painters of Montparnasse draws Louise, alongside Roman Ketoff, an attractive and maverick journalist into the dark underbelly of high society, and forces her to confront certain truths about those she thought she knew well. In order to infiltrate the Parisian bohemian nightlife and to protect her identity, she creates another character, a flamboyant and glamorous female alter ego of herself, Gisele. Louise is now investigating as a man by day and as a woman by night.