"The Horla" by Guy de Maupassant is a gripping tale of psychological horror that explores themes of madness, invisible influence, and the supernatural. Through the diary entries of the protagonist, readers are plunged into his descent into paranoia, as he becomes convinced that an invisible being, the Horla, is haunting and controlling him. Maupassant masterfully blurs the lines between reality and hallucination, leaving readers questioning the nature of the protagonist's torment.