The narrator arrives at the House of Usher at the request of his childhood friend, Roderick Usher, who is suffering from a mental illness. The house is creepy, like it is surrounded by an unusual atmosphere.
The narrator tries to cheer up Roderick Usher, and he learns that Usher's twin sister just died of the same illness that Usher has. They place her in a coffin inside the mansion. Secretly, the narrator is starting to believe in the darkness that Usher tells him about.
Roderick Usher and his twin sister, Lady Madeline, both struggle with a mental illness. The narrator goes and tries to comfort Usher.
In the middle of a very stormy night, Usher and the narrator realize that Lady Madeline wasn't actually dead. She walks through the door, collapses on Usher, and both of the twins die.
The narrator flees the mansion, terrified.
As the narrator looks back, the mansion collapses. This symbolizes the actual House of Usher collapsing and the family of Usher no longer existing because they all died.