Detective Dupin is introduced. He lives in an apartment with one of his friends. He feels more comfortable in the night and keeps his apartment dark. He solves crimes to test his skill and logic.
Dupin finds out that a woman by the name of Madame L'espanye has been brutally murdered. Witnesses reported hearing shrieks coming from the home and Madame L'espanye is found stuffed up a chimney
Dupin receives depositions from many people who have information about the case. Dupin then goes on to find fingernails and hair among the crime scene. Le Bon had been arrested for carrying money for Madame L'espanye and is a prime suspect.
After further investigating the case, Dupin comes to the conclusion that an oranguatang had killed Madame L'espanye. It is also discovered that this primate belonged to a sailor and that Dupin would speak with him.
The sailor explains how the Ourang-Outang had escaped during the night and was attracted toward the light of L'espanaye's apartment. The sailor had seen the murders, but he thought he would get blamed for them if he spoke up.
The sailor is able to find his Ourang-Outang and sell him away. Le Bon is released from jail as he is not the one who committed the murder. Dupin's work has been completed.