Our main character arrived at the mansion of his old childhood friend after receiving a letter from the friend asking him to visit because he(the friend) is sick.
We find Usher on a sofa who, because of how sick he is, had the complexion of a corpse. And we learn that his symptoms are his overly acute senses hurting him, but that the main reason for his poor health being his sickly sister, his last living relative, who is likely close to death
The narrator spent the next few days with Usher trying to distract him from his sister's condition
After a period of time, the narrator is informed that Lady Madeline(the sister) has died, and that Usher wanted to keep her encoffined in one of the vaults in the mansion for the doctors to study.
Usher's condition worsened after the death. After a week after Madeline's "death", our narrator couldn't sleep one night and Usher entered the room. They see glowing light and vapor around them, the narrator assuring him that it's just because of the weather, and reading a book to distract Usher.
As our protagonist read the book out loud, we hear sounds fitting what he describe from the floor below. Usher with a creepy smile starts muttering about how he knew that she is alive, that his acute sense made him hear her moving around in the coffin. He screamed at the door which opens showing Lady Madelaine with a bloody robe who then fell on him, both of them now dead.