Because he is due to die the next day, the narrator has decided to present the facts of a past event that has terrified and destroyed him, although he claims that he is not mad and hopes that someone else will be able to explain his story logically. He begins by describing his kind and humane younger self: he keeps many pets because animals such as dogs are so loving and faithful, and at a young age he marries a woman who also loves pets. In their household they have a number of animals, including a large and beautiful black cat named Pluto. Although his wife often refers to the superstition that black cats are actually disguised witches, the narrator is particularly fond of the unusually intelligent cat.
In subsequent years, the narrator becomes increasingly moody and irritable due to alcoholism, and he begins to verbally abuse and threaten his wife as well as his pets. He remains less harsh to Pluto until one day, when he comes home drunk and, imagining that Pluto is avoiding him, he seizes the cat, which bites him on the hand in fear. In response, the narrator loses control and cuts one of Pluto's eyes out with a pen-knife. After sobering up the next morning, he feels a modicum of remorse but returns to drinking. The cat recovers, but it conspicuously avoids its owner, who is at first grieved and later annoyed and provoked. He describes it as a primitive impulse of perverseness that drives him to complete his attack on Pluto by hanging the cat from a tree, although he cries as he does the deed, aware that he has committed a deadly sin on an animal that once loved him.
The same night as the cat's death, the house is set on fire, and the narrator, his wife, and his servant barely escape, although he is left with little wealth. Peculiarly, on the single wall that did not fall in the fire is an image of a gigantic cat with a rope around its neck. The narrator explains the phenomenon away, reasoning that someone must have thrown the cat into his window to try to wake him up in the fire and that as other walls fell, they must have compressed the animal into the plaster, where the lime, the heat, and the ammonia from the cat's body combined to form the image. However, he remains disturbed and feels a sense of regret that falls just short of remorse.
For months, the narrator searches for a replacement cat, which he discovers while drinking. The new cat resembles Pluto except for a patch of white hair on its chest. The landlord has never seen the animal before, and the cat takes a liking to the narrator, who brings it home. His wife becomes fond of the cat, but the narrator is increasingly annoyed with the cat's affection towards him, and his annoyance turns into hatred. He begins avoiding the cat, although his shame about his previous cruelty prevents him from being violent towards it. His hatred of the animal increases until one day the cat loses one of its eyes. This endears it even more to his loving wife, who has retained the kindness that the narrator admits he used to have.
In spite of the narrator's dislike for the cat, it follows him everywhere, and he begins to dread the cat, which he calls a "beast." As his wife often points out, the cat bears a distinct resemblance to Pluto, except for the white patch that the narrator notes has gradually come to resemble a gallows. The narrator fearfully explains that he has lost what was left of his former goodness, and he indulges in hatred and fury, although his wife never complains.
At one point, when the protagonist and his wife enter their cellar, the cat trips him. Enraged, he starts to take an axe to the cat, but his wife's hand stops his arm. Furious at her interruption, he strikes her head with the blade, killing her instantly. Realizing that he cannot remove the body from the house, he considers ways to conceal it, including cutting it up and burning it, digging a grave in the cellar, throwing the corpse into the well, and packing it up in a box and having it carried out of the house under the guise of merchandise. Eventually he decides to wall it up with plaster in the cellar behind a false fireplace, leaving no evidence of the deed. The narrator tries to find the cat so he can kill it, but the animal is nowhere to be found, and he sleeps well that night, free of guilt.
On the second and third days, the cat does not appear, inspiring relief in the narrator, but on the following day, policemen come to investigate. The narrator calmly cooperates, and the policemen find nothing, despite searching the cellar multiple times. The narrator bids the police farewell, but in a fit of bravado, he mentions that the walls of the house are sturdily constructed, and with a cane, he raps on the wall that hides his wife.
A cry emanates from behind the wall, evolving from a muffled, broken sob into an inhuman scream. Seeing that the game is up, the narrator staggers away from the wall, and after pausing from terror and awe, the police disassemble the wall and find the cat "with red extended mouth and solitary eye of fire" sitting on the head of the corpse. The narrator realizes, to his horror, that he must have trapped the cat behind the wall along with his wife.
"The Black Cat" bears close similarities with the story of the "The Tell-Tale Heart" in that it begins with an unnamed narrator who has been apprehended for murder and who insists that he cannot be insane before he begins an account of a murder that he committed. Unlike "The Tell-Tale Heart," however, we have a man who is aware of the transformation in himself that has led him to become a murderer, although he cannot totally explain it, and we even have a potential cause for his insanity in the form of alcohol. Whereas the protagonist of "The Tell-Tale Heart" explains his case for murder as if his logic were obvious and inevitable, the narrator of "The Black Cat" is on some level aware of his unreasonableness, although he chooses to ignore it and succumb to the baser human emotions of perversity and hatred.
One aspect of the narrator's personality that he shares with several of Poe's characters is that despite his overall lack of normal ethics and good judgment, he uses some reason and logic to avoid admissions of his mental abnormality. In particular, when he sees the image of his cat on the one remaining wall of his house after it burns down, he tries to ignore superstition and offer a reasonable, scientific explanation for its existence. Ironically, the only superstitious member of his household is his wife, who consistently shows a strong moral character despite the abuses and deterioration of her husband. Given that in "The Tell-Tale Heart" the narrator's main proof of his sanity is his rational mind, the contrast between the wife and husband in "The Black Cat" suggests that the difference between a normal mind and an unhealthy one is that the unhealthy mind uses logic to explain away what a normal mind would intuitively understand. Rather than allowing himself to use his wits to recognize the possible significance of the cat's image on the wall, he convinces himself of the scientific explanation in order to forestall thinking about his guilt.
The supernatural elements of "The Black Cat" leave open the question of how much is real, how much can be rationally explained, and how much is a product of the narrator's imagination. Pluto's possible magical significance is first noted by the wife, who states that black cats are said to be witches in disguise, although her kind treatment of Pluto indicates that she does not put much faith in this particular superstition. The narrator explicitly dismisses this viewpoint, but the superstition flavors his entire story. When he observes the image of the cat on the wall, he describes it as gigantic; he previously described Pluto as fairly large, but whether the size of the image is an expression of the paranormal or simply a product of his frightened imagination is difficult to say. Similarly, the narrator claims that the patch of fur on the cat transforms from an "indefinite splotch" to the specific image of the gallows, but we have no evidence that the narrator is observing anything more than the twisting of his own mind.
The narrator speaks specifically about the spirit of perverseness that combines with his alcohol dependence to provide the impetus for his transformation into a murderer. He is particularly careful to explain how perversity drives him to hang his cat Pluto, and at the time, he understands the evil of his crime and even feels some measure of guilt over it. The sign of his decreasing sanity comes as much from his lack of guilt over killing his wife as it does from the actual act of burying his axe in her skull. His explanation that perverseness is "one of the primitive impulses of the human heart" is called into question because of his madness, but at the same time, the story makes us wonder about the truth of his assertion. On the one hand, perverseness might seem natural to the narrator precisely because he was already prone to it, despite what he claims was his previously innocent personality. On the other hand, perhaps he is correct in that perversity exists in all men but is merely aggravated in him.
"The Black Cat" is in many ways a moral tale that deals with the tension between love and hate and that warns of the dangers of alcohol, a substance to which Poe himself was addicted for much of his life. The narrator appears at first to love both his wife and his pets, but by the end of the story his fondness has turned to neglect, spite, and even hatred, particularly for Pluto and his successor. Although Poe does not provide a solid explanation for the narrator's encroaching loss of sanity, perhaps suggesting that madness might happen at any time to any person, the narrator admits the role of alcohol in his behavior. In addition, the arrival of the second cat is closely related to his alcoholism, since he first finds the cat in a seedy drinking establishment. The second cat ultimately serves as the facilitator of justice when it reveals the corpse's hiding place at the end of the tale, and its initial appearance on top of a hogshead of gin or rum emphasizes its moral purpose.