The unnamed narrator of the story lives alone in a dark, ancient castle surrounded by a dense forest. He never sees sunlight, and he has no memory of human contact. One day, desperate to see the sun, the narrator decides to climb the ruined tower which is the only part of the castle taller than the trees. After the dangerous climb to the top room of the tower, the narrator is delighted to see the moon through a grating. Soon, however, he discovers the horrible truth behind his confinement.
Although it is not part of the Cthulhu Mythos for which Lovecraft is best known,"The Outsider" is one of the most popular and frequently anthologized tales by the author. The story is generally considered among Lovecraft's works to be the closest in style to the classic tales of horror by Edgar Allan Poe.
The unnamed narrator does not know where he was born. He only remembers the ancient and dark castle where he believes he must have lived for years. The castle is surrounded by tall trees so that no sunlight reaches it. There is one tower which is taller than the trees, but it is ruined and can only be ascended by climbing up the stone wall.
The narrator does not recall ever having been with people. The only company he has, other than such creatures as rats and spiders, are bones and skeletons in the underground crypts of the castle. He has learned all he knows from books. He does not remember hearing anyone speaking, and he never speaks aloud himself. He does not know how old he is, although he suspects he is young because he does not remember much. There are no mirrors in the castle so he imagines he looks similar to the illustrations of youths he has seen in books.
The narrator has tried to go beyond the dark forest surrounding the castle, but found it grew denser and darker the farther he went. One day his longing for light finally becomes so great that he decides to risk his life and climb the ruined tower. He ascends the stone stairs as far as they go then begins to climb the wall, clinging to small holds in the dark. After a long, slow crawl up the tower, his head finally comes up against a barrier, perhaps a trapdoor. He manages to push it up and crawl through the opening. The heavy slab falls down blocking his way back.
The room is dark. The narrator gropes around until he finds a stone door. It is locked, but he forces it open with a mighty effort. He is rewarded with the sight of the full moon through a grating at the end of the passageway. He opens the grating carefully expecting to see treetops at some distance below. He is shocked to see instead the solid ground stretching before him. The narrator staggers out and finds himself among the marble slabs and columns on the grounds of a ruined stone church. Driven by the desire to see people, he stumbles along the gravel path and goes out through an arch into open country.
After two hours of wandering, the narrator comes upon a castle in a wooded park. The castle looks oddly familiar to him, although it appears to have new wings and some towers have been demolished. Delighted to see open windows, he looks into the brightly lit room. He sees a party of strangely-dressed people making merry. He enters the room through the low window. Suddenly, everyone begins to scream and flee. The narrator stands in a daze, not knowing what has caused the panic. Fearing there is something terrible lurking nearby, he begins to walk towards the arched doorway leading to another room.
As he approaches the arch, the narrator detects a presence. When he finally sees what everyone else must have seen, he is horrified into near paralysis. The ghoulish monstrosity, a hideous carrion still retaining some outline of the human shape, stares at the narrator with its glassy eyes. In his attempt to flee, the narrator loses his balance and staggers forward. As he extends his arm to ward off the creature, his fingers come in contact with the monster's paw.
In that second, the narrator's memory comes flooding back to him, and he recognizes the abomination standing in front of him. He runs back to the churchyard and finds the stone trapdoor immovable. Although he is now doomed to roam in the darkness, the narrator prefers the newfound freedom to the confinement of the ancient castle. He has also come to accept his alienation. He knows that he is an outsider, a stranger who does not belong – because what his fingers touched was not a creature but "a cold and unyielding surface of polished glass."
The American film Castle Freak written and directed by Stuart Gordon is loosely based on "The Outsider". The film was released directly to video on November 14, 1995.
There have been multiple short-film adaptations of "The Outsider" made by students and other amateur filmmakers. The story has also been adapted as a radio play.