The Cask of Amontillado is a short story chronicling the gruesome revenge of one man, Montresor, on another, Fortunato. Compelled by perceived slights, Montresor tempts the drunken Fortunato into his basement with the promise of the titular wine, an exquisite vintage. There he chains him to a wall and bricks him up within it, immuring him. The story handles themes of revenge, lack of empathy, cruelty, and the ability to live in a state of guilt represented by Montresor's getting away with his crime.
The story's narrator, Montresor, tells the story of the day that he took his revenge on Fortunato (Italian for "the fortunate one"), a fellow nobleman, to an unspecified person who knows him very well. Angry over numerous injuries and some unspecified insult, he plots to murder his "friend" during Carnival when the man is drunk, dizzy, and wearing a jester's motley.
Montresor lures Fortunato into a private wine-tasting excursion by telling him he has obtained a pipe (about 130 gallons, 492 litres) of what he believes to be a rare vintage of amontillado. He mentions obtaining confirmation of the pipe's contents by inviting a fellow wine aficionado, Luchesi, for a private tasting. Montresor knows Fortunato will not be able to resist demonstrating his discerning palate for wine and will insist that he taste the amontillado rather than Luchesi who, as he claims, "cannot tell Amontillado from Sherry". Fortunato goes with Montresor to the wine cellars of the latter's palazzo, where they wander in the catacombs. Montresor offers wine (first Medoc, then De Grave) to Fortunato in order to keep him inebriated. Montresor warns Fortunato, who has a bad cough, of the damp, and suggests they go back; Fortunato insists on continuing, claiming that "[he] shall not die of a cough." During their walk, Montresor mentions his family coat of arms: a golden foot in a blue background crushing a snake whose fangs are embedded in the foot's heel, with the motto Nemo me impune lacessit ("No one attacks me with impunity").
At one point, Fortunato makes an elaborate, grotesque gesture with an upraised wine bottle. When Montresor appears not to recognize the gesture, Fortunato asks, "You are not of the masons?" Montresor says he is, and when Fortunato, disbelieving, requests a sign, Montresor displays a trowel he had been hiding. When they come to a niche, Montresor tells his victim that the amontillado is within. Fortunato enters drunk and unsuspecting and therefore, does not resist as Montresor quickly chains him to the wall. Montresor then declares that, since Fortunato won't go back, Montresor must "positively leave" him there.
Montresor reveals brick and mortar, previously hidden among the bones nearby, and walls up the niche, entombing his friend alive. At first, Fortunato, who sobers up faster than Montresor anticipated he would, shakes the chains, trying to escape. Fortunato then screams for help, but Montresor mocks his cries, knowing nobody can hear them. Fortunato laughs weakly and tries to pretend that he is the subject of a joke and that people will be waiting for him (including the Lady Fortunato). As the murderer finishes the topmost row of stones, Fortunato wails, "For the love of God, Montresor!" to which Montresor replies, "Yes, for the love of God!" He listens for a reply but hears only the jester's bells ringing. Before placing the last stone, he drops a burning torch through the gap. He claims that he feels sick at heart, but dismisses this reaction as an effect of the dampness of the catacombs.
In the last few sentences, Montresor reveals that 50 years later, Fortunato's body still hangs from its chains in the niche where he left it. The murderer concludes: In pace requiescat! ("May he rest in peace!").