''The Murders in the Rue Morgue'' takes place in Paris and is related by an unnamed narrator. The tale begins with a somewhat complicated discussion about the differences between those who are clever or ingenious and those who are truly analytical or rational and explains that the glory of being analytical is at the heart of the story that follows. We learn that the speaker and a close friend of his, Monsieur C. Auguste Dupin, live a secluded life together. One evening while walking through the city, Dupin and the narrator read a story in a newspaper about the gruesome and unsolved death of Madame L'Espanaye and her daughter, Mademoiselle Camille L'Espanaye. Madame L'Espanaye's neck has been cut so deeply that her head falls off when police pick her body up, and Mademoiselle Camille L'Espanaye is found stuffed in a chimney. Although a variety of witnesses all report hearing two or more voices, none of them can agree on what language the voices were speaking. Police are baffled by the crime and, despite any conclusive evidence, arrest a man named Adolphe Le Bon.
Dupin shows little interest in the case until he learns that Le Bon, a friend of his who had done him a favor in the past, is accused of the crime. After the narrator and Dupin visit the crime scene, Dupin points out that the police have overlooked important clues, including the presence of a non-human hair and the possibility that the voice the witnesses heard might not be human. With this evidence, Dupin describes how the perpetrator is most likely an escaped orangutan. Dupin then reveals that he has already placed an advertisement in a newspaper explaining that he has found an orangutan and the owner can come collect him.
The story culminates with the appearance of a sailor who, responding to Dupin's advertisement, has come to collect his orangutan. The sailor then relates that after escaping from his owner with a shaving razor, his pet climbed into Madame L'Espanaye's room. Mimicking his master's habit of shaving his face, the orangutan accidentally slices her throat, and, excited by the blood, chokes Mademoiselle Camille L'Espanaye to death and escapes out the window. The miraculous conclusion to the story, moreover, refers back to the opening discussion about the importance of being analytical, for the main policeman wasn't able to solve the crime because he was merely ingenious and not analytical.