What is the plot of the Cask of Amontillado?

The story is narrated by Montresor, who carries a grudge against Fortunato for an offense that is never explained. Montresor leads a drunken Fortunato through a series of chambers beneath his palazzo with the promise of a taste of Amontillado, a wine that Montresor has just purchased. When the two men reach the last underground chamber, Montresor chains Fortunato to the wall, builds a new wall to seal him in, and leaves him to die.