In 19th-century Paris, a scene of pure horror unfolds, described by the narrator as a story that will "make your blood run cold." On a "dark and foggy night," the tranquility of the city is shattered by a "terrifying scream." Witnesses report hearing two distinct voices from an apartment: one identifiable as French, and another that is "high-pitched" and unintelligible. Upon bursting into the apartment with "great force," bystanders are confronted with a "horrific sight." The scene is characterized by total chaos; a woman's body is discovered "hanging from the chimney," while another lies in the courtyard with "blood running from a cut in her neck." Despite the violence, "two bags of money" remain untouched, deepening the mystery.
The investigation faces a significant hurdle: the "windows are closed" and the "doors are locked." Furthermore, witnesses report that "no one saw anyone run down the stairs" as they ascended, creating a classic locked-room enigma. The local police find themselves unable to process the evidence, as they have "never run up against something like this before." This necessitates the intervention of a "super sleuth"—the brilliant private detective, Dupin.
Dupin approaches the case by meticulously running through "all the possible scenarios" in his head. He focuses on the key constraints: the "strange voice," the brutality of the perpetrator, and the lack of a conventional "means of escape." During his forensic examination, he identifies "handprints on the woman's body" that are "large and possibly not human." This realization shifts his hypothesis toward the involvement of an animal, specifically an "ape."
Dupin theorizes that the high-pitched voice belonged to the owner of the ape, who feared being "blamed for the ape's behaviour." Rather than "run the risk of losing" the suspect, Dupin uses a clever ruse: he advertises for the owner of a lost animal. This strategy proves successful, leading the sailor to "confess what happened on that tragic night."
The sailor reveals a harrowing chain of events: the ape had been playing with a "razor" before escaping. Attracted by the "light in the victim's window," the animal climbed the building. When the woman screamed, the ape panicked, resulting in the "gruesome" murders. The ape killed the woman by cutting her throat and then strangled her daughter. The animal subsequently escaped through the window, which shut behind him, leaving the sailor "traumatised" and unable to intervene.
Through his superior deductive reasoning, Detective Dupin manages to "get to the bottom of this murder mystery." The narrative concludes with the capture of the ape, which was eventually "sold to a zoo." By solving this complex case, Dupin restores order, ensuring that the citizens of Paris can "sleep safely tonight." This case serves as a quintessential example of how analytical thinking can unravel even the most chilling and inexplicable crimes.