"L'Affaire Lerouge" is a novel written by the French author Émile Gaboriau. First published in 1866, it is considered one of the early works of detective fiction and played a significant role in shaping the genre. The novel is centered around the mysterious murder of a widow named Widow Lerouge. As the investigation unfolds, we follow the work of the detective Frédéric Larsan, who is determined to solve the case. The story takes place in a small French village, and the murder leads to a web of secrets, suspicions, and hidden identities. Émile Gaboriau's "L'Affaire Lerouge" is notable for introducing key elements of detective fiction that would later become staples of the genre, including a brilliant detective, a puzzling crime, and the unraveling of clues. The novel laid the foundation for subsequent mystery and detective stories. Keywords: Émile Gaboriau, "L'Affaire Lerouge," detective fiction, mystery, murder, investigation, hidden identities, early detective stories.