It is a recording of a dream, where the main protagonist is a Roman military official in the Basque country near Pompelo. The countryside is, every year, ravaged by terrible hill people who kidnap citizens and perform cruel rituals at a Sabbath. The narrator wishes to lead a military expedition to crush these hill folk, as a feeling of approaching evil has enveloped the countryside, due to a riot between the citizens and the hill people. These hill folk came to trade, yet some of these are killed and later, no disappearances occur before the time of the Sabbath. The incursion is guided by a local-born son of Roman parents.
Carter, a weird fiction writer, meets with his close friend, Joel Manton, in a cemetery near an old, dilapidated house on Meadow Hill in the town of Arkham, Massachusetts. As the two sit upon a weathered tomb, Carter tells Manton the tale of an indescribable entity that allegedly haunts the house and surrounding area. He contends that because such an entity cannot be perceived by the five senses, it becomes impossible to quantify and accurately describe, thus earning itself the term unnamable. As the narration closes, this unnamable presence attacks both Carter and Manton. Both men survive and awaken later at St. Mary’s hospital. They suffer from various lacerations, including scarring from a large horn-shaped object and bruises in the shape of hoof-prints on their backs.
The story involves a mine that uncovers a very deep chasm, too deep for any sounding lines to hit bottom. The night after the discovery of the abyss the narrator and one of the mine's workers, Juan Romero, venture inside the mine, drawn against their will by a mysterious rhythmical throbbing in the ground.
The story tells of an unnamed narrator, who has moved from New England to New York City and greatly regretted it. One night, while wandering an older part of Greenwich Village, he happens upon a man strangely dressed in garments from the eighteenth century. The man offers to show the narrator the secrets of the town.
The story is about a golden-haired youth who wanders into the city of Teloth, telling tales of the great city of Aira, where he was prince. While Iranon enjoys singing and telling his tales of wonder, few appreciate it. When a disenfranchised boy named Romnod suggests leaving Teloth to go to the famed city of Oonai (which he thinks may be Aira, now under a different name), Iranon takes him up on his offer.
The unnamed narrator describes the final fate of his good friend, Denys Barry, an Irish-American who reclaims an ancestral estate in Kilderry, a fictional town in Ireland. Barry ignores pleas from the local peasantry not to drain the nearby bog, with unfortunate supernatural consequences.
The narrator, hearing tales of a "lurking fear" upon Tempest Mountain in the Catskills, takes two men with him to investigate. They camp inside the deserted Martense mansion as a lightning storm approaches, and feeling strangely drowsy, they all fall asleep. The narrator wakes up to find both his companions missing, and in a flash of lightning sees a demonic shadow cast upon the fireplace chimney from a grotesque monster like the other one.