The narrator of the story kills his first cat, Pluto, in a fit of rage. This first cat then seems to haunt the narrator from beyond the grave. The night after the cat’s death, the narrator’s house burns down. On the next day, he sees the figure of a gigantic cat, with a rope around its neck, impressed upon a surviving wall, “as if graven in bas relief upon the white surface.”
A little while later, the narrator begins to feel remorseful, and starts to search “among the vile haunts which (he) now frequent(s)” for a cat similar to the one he killed. The implication is that the narrator wants to find a new, replacement cat so that he can treat it better than he treated the first cat. In treating the second cat more kindly, the narrator perhaps hopes to ease his conscience, and temper the guilt he feels because of his cruel treatment of the first cat.
The narrator then happens upon a cat which looks remarkably like the first cat, except that the new cat has a large “splotch of white” covering its breast, whereas the first cat was entirely black. As the story continues the new cat seems to be a reincarnation of the first cat, come back to life to haunt and terrorize the narrator. The second cat (or rather the reincarnation of the first cat) drives the narrator to madness, and the madness consumes the narrator until he kills his wife by burying an axe in her head. At the end of the story, the narrator blames this second cat for “seduc(ing) (him) into murder” and thus “consign(ing) (him) to the hangman.” This is of course a fitting revenge for the reincarnation of the first cat that the narrator hanged from a tree.