The Cask of Amontillado is narrated by Montresor, who opens by declaring that he has endured a thousand injuries from a man named Fortunato, but that a recent insult has finally driven him to seek an irreversible revenge. He vows that he will punish Fortunato decisively, without suffering any consequences himself, and that his enemy will know exactly who is responsible for his fate. Montresor reveals nothing about the specific nature of the insult, leaving the reader to wonder whether his grievance is legitimate or wildly exaggerated.
The story takes place during the frenzy of carnival season in an unnamed Italian city. Montresor encounters Fortunato on the street. Fortunato is dressed in the motley costume of a court jester, complete with a cap of bells, and he is already quite drunk from the evening's celebrations. Montresor seizes the opportunity by mentioning that he has recently acquired a cask of rare Amontillado sherry, but confesses that he has doubts about its authenticity. He suggests he might ask a mutual acquaintance named Luchesi to examine it instead. Fortunato, who prides himself enormously on his expertise in fine wines, is immediately offended at the thought of Luchesi being consulted and insists on tasting the Amontillado himself.
Montresor leads Fortunato through the streets to his family palazzo, which is empty because all the servants have slipped away to enjoy the carnival. The two men descend into the damp, sprawling catacombs beneath the building, which serve as both wine cellars and a burial vault for generations of Montresor's ancestors. The walls are lined with nitre, a white mineral crust that speaks to the overwhelming moisture and decay. As they walk deeper underground, Fortunato develops a persistent cough from the damp air. Montresor repeatedly expresses concern for Fortunato's health and suggests they turn back, but these gestures of solicitude are entirely calculated. Each time Montresor offers to leave, Fortunato stubbornly refuses, driven forward by his pride and his desire to prove his superior palate. Along the way, Montresor offers Fortunato more wine to drink, keeping him intoxicated and compliant.
During their descent, Montresor mentions his family's coat of arms: a golden foot crushing a serpent whose fangs are embedded in the heel, with the motto "Nemo me impune lacessit," meaning "No one provokes me with impunity." This heraldic detail serves as a veiled warning that Fortunato, deep in his cups, completely fails to recognize. The catacombs grow narrower and darker as they penetrate further into the earth, the piles of bones from ancient burials pressing in on either side.
At last they reach a small recess at the deepest point of the vaults. Montresor tells Fortunato the Amontillado is inside. When Fortunato steps into the narrow alcove, bewildered and disoriented by drink, Montresor acts swiftly. He chains Fortunato to a pair of iron staples embedded in the granite wall. Before his victim can fully comprehend what is happening, Montresor begins laying a wall of stone and mortar across the entrance to the recess. He works methodically, tier by tier, sealing Fortunato inside.
As the wall rises, Fortunato's drunkenness fades and the terrible reality sets in. He begins to scream and struggle against the chains. Montresor pauses to listen, even pressing himself against the wall to enjoy the sounds. At one point, Fortunato tries a different approach and laughs weakly, suggesting the whole affair must be a joke and that they will have a good laugh about it later over wine. Montresor agrees that yes, they will indeed laugh. But the wall continues to rise. In the final moments before the last stone is placed, Fortunato calls out Montresor's name twice in a plaintive, desperate voice. Then there is silence. Montresor calls into the darkness but receives no answer except the faint jingling of the bells on Fortunato's jester cap.
Montresor fits the last stone into place and plasters over the wall. He restacks the bones of the dead against it so that no one will ever discover what lies behind. The story ends with Montresor revealing that for fifty years no one has disturbed the remains. His final words, "In pace requiescat" — may he rest in peace — carry a tone that has been debated endlessly: is it genuine remorse, or one final sardonic flourish from a man who has never regretted what he did?