The narrator and the old man live in this house. For seven nights, the narrator enters the room of the old man.
He takes a lantern and shines it upon his deformed eye, which is closed on the first seven nights.
On the eighth night, the eye is open and the old man knows the narrator is in the room. The narrator walks across the room and throws him off the bed, causing him to scream.
Once the old man started to scream, the narrator threw his mattress upon him and killed the old man!
Once the narrator killed the old man, he hid him under the floorboards and made the bed neatly so nobody would suspect he did anything.
The police arrive at the narrator's house, summoned by a neighbor who heard the old man scream. The narrator originally lies and says that nothing was happening, but later as the policemen were talking he owned up to his deed.