The narrative begins in Paris, where the narrator meets C. Auguste Dupin, a man of noble lineage reduced to poverty who survives on meager funds while devoting himself entirely to books and midnight strolls. Their shared intellectual curiosity leads them to rent a decaying, secluded house together, where they adopt a nocturnal lifestyle and spend hours engaged in mutual analysis. Dupin demonstrates an astonishing capacity for deduction by effortlessly tracking the narrator's unspoken thoughts through a chain of seemingly random street observations.
Soon, the Parisian press reports a sensational and gruesome double murder on the Rue Morgue involving Madame L'Espanaye and her daughter Camille. The victims are found in a locked fourth-floor room bearing horrific injuries, with the mother's throat slashed and the daughter shoved headfirst up a chimney, while four thousand francs in gold remain untouched. Eyewitnesses give contradictory testimonies regarding the strange, inhuman voices heard at the scene, and police investigators find themselves utterly unable to explain how the murderer escaped from a sealed room with no accessible exits.
Intrigued by the total lack of apparent motives and the bizarre physical details of the crime, Dupin secures permission from the police prefect to examine the gruesome crime scene himself. After a thorough inspection of the room, the windows, and the courtyard, Dupin concludes that the crime defies conventional human explanation and deduces that the perpetrator possessed extraordinary agility, superhuman strength, and a foreign, non-human voice. He places a classified advertisement in a maritime newspaper regarding a captured orangutan, successfully drawing its owner to their apartment to claim the animal. The visitor, a terrified sailor, arrives and confesses the entire truth of the incident to avoid suspicion. He explains that the escaped orangutan climbed a gas pipe into the Rue Morgue apartment, where it mimicked the razor-wielding actions of a human and flew into a blind, destructive rage that ended in the horrific murders when startled by the victims. With the mystery completely resolved through Dupin's rigorous analytical method, the innocent clerk Adolphe Lebon is promptly released from prison, and the captured ape is eventually sold to a menagerie.
