The narrator starts off by telling the reader that he is not crazy, but nervous and diseased and can says how calmly he can tell the whole story. He proceeds to say that he wanted to kill the Old Man because he had the eye of a vulture. The story takes place in the Old Man's house at midnight.
He continues by telling us that he had nothing against the old man and how he was never kinder to the old man than in the week before he killed him. The narrator states how every night for eight days he would look in to watch the old man sleep and open a lantern to see if the eye was open. The next morning he would ask how he slept to figure out if the man sensed anything.
On the eighth night, the narrator is overly confident and wakes the man up but still continues into the room. The old man cries out "who's there" which leads to neither of them moving a muscle for an entire hour. Next the narrator opens the lantern so a tiny ray of light shines out into the vulture eye. This leads to the narrator hearing " a low, dull, quick sound and thinks it is the old mans "hideous heart". He keeps saying how it is getting louder. The narrator says a new anxiety seizes him; he is afraid the beating will be heard through the wall. "
When he realizes the sound might be heard through the wall, he makes his move and leaps into the room, smothering the old man with a mattress. The narrator dismembers the body in the bathtub to eliminate the risk of there being blood stains.
He places the corpse under the floor boards and the moment he is done the police arrive at the door because one of the neighbors said they heard a shriek.
The police search the house and the narrator invites them to rest inside. He places his chair directly above the floorboard where the corpse is. He has a normal conversation with the police but he hears a beating in his ears and the more he tries to stop it the louder it gets. He finally can't take it anymore and says, "tear up the planks! here, her! --It is the beating of his hideous heart!"