The unnamed narrator of the story opens with a lengthy commentary on the nature and practice of analytical reasoning, then describes the circumstances under which he first met Dupin during an extended visit to Paris. The two share rooms in a dilapidated old mansion and allow no visitors, having cut off all contact with past acquaintances and venturing outside only at night. "We existed within ourselves alone," the narrator states. One evening, Dupin demonstrates his analytical prowess by deducing the narrator's thoughts about a particular stage actor, based on clues gathered from the narrator's previous words and actions.During the remainder of that evening and the following morning, Dupin and the narrator read with great interest the newspaper accounts of a baffling double murder. Madame L'Espanaye and her daughter have been found dead at their home in the Rue Morgue, a fictional street in Paris. The mother was found in a yard behind the house, with multiple broken bones and her throat so deeply cut that her head fell off when the body was moved. The daughter was found strangled to death and stuffed upside down into a chimney. The murders occurred in a fourth-floor room that was locked from the inside; on the floor were found a bloody straight razor, several bloody tufts of gray hair, and two bags of gold coins. Several witnesses reported hearing two voices at the time of the murder, one male and French, but disagreed on the language spoken by the other. The speech was unclear, and all witnesses claimed not to know the language they believed the second voice to be speaking.A bank clerk named Adolphe Le Bon, who had delivered the gold coins to the ladies the day before, is arrested even though there is no other evidence linking him to the crime. Remembering a service that Le Bon once performed for him, Dupin becomes intrigued and offers his assistance to "G-", the prefect of police.Because none of the witnesses can agree on the language spoken by the second voice, Dupin concludes they were not hearing a human voice at all. He and the narrator examine the house thoroughly; the following day, Dupin dismisses the idea of both Le Bon's guilt and a robbery motive, citing the fact that the gold was not taken from the room. He also points out that the murderer would have had to have superhuman strength to force the daughter's body up the chimney. He formulates a method by which the murderer could have entered the room and killed both women, involving an agile climb up a lightning rod and a leap to a set of open window shutters. Showing an unusual tuft of hair he recovered from the scene, and demonstrating the impossibility of the daughter being strangled by a human hand, Dupin concludes that an "Ourang-Outang" (orangutan) killed the women. He has placed an advertisement in the local newspaper asking if anyone has lost such an animal, and a sailor soon arrives looking for it.