Diary of a Madman

Following Simon Cordier's funeral, his secret diary is read aloud to a circle gathered around a table by the pastor. The diary reveals that Cordier has encountered a malevolent entity called the horla. It is described as capable of limited psychokinesis and mind control, a creature that may belong to a race devoted to driving humans insane.

Cordier is drawn into an encounter with a prisoner the horla has driven to murder four people. The horla possesses the inmate and tries to kill Cordier, but he kills the man in self-defense. The incident marks the horla's first direct pressure on Cordier's life.

Haunting and fear creep into Cordier's life as he worries he is going mad. He seeks help from an alienist, who suggests that taking up a hobby might steady his nerves. Cordier decides to return to sculpture to regain control.

Cordier returns to sculpture and meets Odette Malotte, a married model. He becomes fond of her and pledges his love, but the horla pressures him to view her as dangerous and deceitful. The horla's manipulation distorts Cordier's judgment about her character.

Cordier's perception grows unreliable as the horla twists reality, amplifying jealousy and suspicion. He struggles to distinguish truth from the entity's insinuations and his own desires. The conflict deepens as Odette's image becomes a battleground for control.

In an episode of insanity, Cordier murders Odette with a knife. Her decapitated body is found in the river, and Odette's husband is blamed for the crime. The act confirms that the horla's influence has crossed a dangerous line.

Facing danger to himself and others, Cordier becomes convinced the horla is real and vows drastic action. He lures the horla into his house at night, intending to trap it. He hurls an oil lamp toward the curtains, igniting the house.

The fire consumes the house as Cordier confronts the horla. He succeeds in destroying the entity but pays the ultimate price. The building burns while he sacrifices himself to end the horror.

Back at the table, the diary readers discuss what happened; some believe Cordier was mad and the horla never existed. Others are unsure, suspecting that the horla might truly exist. The priest asserts that wherever evil exists, the horla exists.

The diary explains the horla's nature as an invisible yet corporeal being with mind-control powers. It hints that Cordier's horla is part of a wider race of evil beings. The account emphasizes a lurking, supernatural threat beyond one man's experience.

The horla's influence seems to linger beyond Cordier's death, with the tale's events casting a long shadow over the listeners. The story suggests that such malevolent forces can survive human perception and memory. The circle around the table remains unsettled, unsure of what to believe.

The priest offers a concluding stance: wherever evil exists, the horla exists. The group is left to decide whether this creature truly exists or remains fear's illusion. The film ends with the uneasy sense that some truths lie beyond rational certainty.