The story opens up with images of a lovely setting in France, a place the first-person narrator clearly loves as he sits under his plantain tree watching the boats sail past. The idea of France as a beautiful country, enjoyed by the narrator, continues as he travels to Mont St. Michel. The atmosphere, however, gradually becomes more bleak as supernatural or psychological dread gradually overtakes our narrator, who cannot sleep at night because he is filled with ever more intense fear that an invisible creature called a Horla is trying to kill him.

The narrator in the beginning of the story seems to be a happy, sane, well-balanced, and sensitive man, who ponders the possible presence of the supernatural (or that which is beyond human sensory perception) in rational terms. This makes it all the more sad when he is overtaken by terrors of a predatory monster coming after him, a fear causing him to burn down his own house. What is most striking in the narrator is the juxtaposition of his rationality—for example, he is able to reflect that the Horla is a manifestation of every person's hidden fear of premature death (hence a psychological problem) with his overwrought and irrational solution to his problem of fearing death: suicide. Maupassant was a master of irony and no doubt enjoyed that ending.

Maupassant’s 1887 horror short story "The Horla" is written in the form of journal entries. The setting is the narrator’s large estate in the country outside Rouen, France. The atmosphere is one of increasing anxiety and unease over four days as the narrator notices strange occurrences that begin when he waves at a Brazilian boat. This seemingly innocent act ushers in an evil presence the narrator calls the Horla. The atmosphere progresses from tense and agitated to hallucinatory and desperate.

The character development of the narrator causes the reader to question his reliability. At first, the evil presence manifests in the form of physical complaints—fever, restless sleep, the feeling of being watched, the sensation of someone kneeling on his chest. The narrator himself questions his sanity as the Horla consumes his thoughts. Whether or not the reader agrees, the narrator concludes that he is sane but continues to feel threatened by the supernatural Horla. The narrator reads an account of strange phenomena in Brazil where people are being terrorized by supernatural creatures and realizes the origin of the creature that brought his suffering. The narrator attempts to cast out the creature by burning his own home and even considers suicide if that would destroy the evil being that may be inside him. This character development relates to themes of questioning reality, perception, and sanity.