Marie-Thérèse, a social worker for an institution known as Le Nid, attempts to rehabilitate Parisian prostitutes. Ignorant of her profession, the artist Pierre falls in love with the streetwalker Marcelle, while his friend René is magnetized by her companion, Maria. When Marcelle's middle-aged friend, the paralyzed Mathilde, is murdered by her former employer, the gangster Ferdinand, the prostitute comes under suspicion. After Ferdinand is killed in an automobile accident, Marie-Thérèse, anxious to clear Marcelle, informs the police that the prostitute was with Pierre at the time of Mathilde's death. Despite police promises to keep all information confidential, Pierre and René learn the truth. Although René accepts Maria, Pierre, disgusted by Marcelle's sordid past, rejects her. The distraught Marcelle is comforted by Marie-Thérèse.