State a theme in the story and explain how it is developed throughout the plot.

Poe's stories usually don't have any deep themes in them. What themes exist are tempered by the mental instability of the protagonist. Still, you might consider the theme of revenge. The force that drives Montresor to commit the horrible murder of Fortunato is his powerful desire for revenge. His first words in the story speak of it: "The thousand injuries of Fortunato I had borne as best I could; but when he ventured upon insult, I vowed revenge." The idea of revenge is repeated several times in the opening paragraph. Montresor will not rush to act, he says, but "at length I would be avenged"; he is determined to "not only punish, but punish with impunity." The terms of the revenge are quite clear in Montresor's mind. He will not feel fully revenged unless Fortunato realizes that his punishment comes at Montresor's hand; a wrong is not redressed "when the avenger fails to make himself felt as such to him who has done the wrong." In seeking revenge, Montresor is acting out the motto of his people, as it appears on the family coat of arms, Nemo me impune lacessit ("No one wounds me with impunity").