Prior to the beginning of the story, the unnamed narrator received a letter from his childhood friend, Roderick Usher, in which Roderick spoke of some illness and expressed his desire to see the narrator.
As the story begins, the narrator arrives at Roderick's home. He is affected by the gloom and melancholy nature of the edifice and its environs. Roderick greets him warmly, and the narrator notes how much Roderick has been altered by his illness; he looks like a cadaver now. Roderick explains the "constitutional and [...] family evil" that affects him so, and he explains that his twin sister, Madeline, suffers from disease as well. The narrator sees Madeline once, from across the room. The old friends pass many days together.
One night, Roderick tells the narrator that Madeline has died and that he would temporarily inter her for two weeks to be sure she is gone. The narrator helps Roderick to entomb her. Within a few days, Roderick's character seems to change; he grows worse and begins to seem hysterical.
About a week after entombing Madeline, the narrator begins to feel quite nervous, and a terrible storm rages outside. He reads to Roderick in the hope of calming him down, but he begins to hear scraping and wailing sounds. Roderick says that he has been hearing it, with his acute senses, for days, and he declares that they have buried his sister alive! Madeline, bloody and reeling, falls upon her brother, and they both perish. The narrator flees and watches as the house splits along a fissure and collapses into the tarn.
1. The narrator approaches the House of Usher and delivers a detailed description of the decaying, melancholy House of Usher, which has “vacant, eye-like windows.” It is in this opening description that the narrator imbues the house with human qualities, and the house starts to become a character itself in the story.
2. Roderick Usher greets the narrator, an acquaintance from his childhood, and the narrator is shocked to discover the sickly state of Roderick, who is emotionally disturbed and complains of a terrible acuteness of his senses. He has called on the narrator for companionship during this dark time. He is deeply depressed and informs the narrator that he and his sister are the last of the Usher kin alive. Many of their ancestors have succumbed (and in this home) to diseases of the mind and body.
3. Roderick explains to the narrator that his sister, Madeline, is sick as well and bed-ridden most of the time. Her ailment is similar to Roderick’s, though she sometimes has cataleptic episodes where she appears to be dead but is really in a temporary coma-like state. The narrator sees her only once (living) as she drifts—mute, unresponsive, ghost-like—through the dark House.
4. Both Madeline and Roderick’s conditions deteriorate, and Madeline succumbs to her illness. The narrator and Roderick put her in a vault in a lower level of the house; Roderick will not contact doctors or undertakers to handle the body, for he fears the scientific establishment will want to pick apart Madeline’s body for research. Before Roderick and the narrator seal Madeline’s coffin, the narrator notes that, because Madeline is so freshly deceased, there is still a bright flush on her cheeks.
5. Roderick’s condition worsens, and the narrator, too, finds himself with heightened senses, especially as a treacherous storm approaches. Roderick asks the narrator to read him the tale of a knight, and as the plot of the story intensifies, the narrator hears terrific noises in the house. As the noises reach a fever pitch, Roderick, in a maniacal state, admits that he has buried his sister alive (thus explaining the flush on her cheeks) and has heard her rustling around in her coffin, scratching to get herself out, for days. The door of the chamber flies open, and Madeline appears, corpse-like and covered in blood. She falls forward onto Roderick, and “[bears] him to the ground a corpse.” They die simultaneously.
6. As the narrator flees the house, the house itself begins to crumble violently and is swallowed up by the “black, lurid” tarn below it. Now that the Usher race has reached its end, the house that seemingly drove many of the Ushers to madness and death, ends with them.
Here is a brief but concise chronology of the story mentioned above:
1. Narrator gets invited to house of Roderick Usher.
2. Narrator arrives, learns about the sickly state of the house and its occupants -- Madeline in particular.
3. Roderick entertains narrator, explains family situation, etc.
4. Madeline goes into cataleptic state, gets entombed alive, returns with bloody clothes.
5. House splits down the center, symbolizing the splitting of the family itself.
As I said, while this is a brief overview of the story's chronology, it in no way intended to be comprehensive. For a more complete chronology, I suggest you visit the summary page for this story in enotes.