An absolutely superb ending, the resolution of the plot of Edgar Allan Poe's "The Cask of Amontillado" enhances further the horror of this Gothic story. While using the Gothic conventions throughout the narrative, Poe subverts these conventions at the end by using only the narrator for the real horror. For, after Fortunato has been deceptively led through a series of ominous and decaying chambers and chained and walled into an area from where there is no escape and his terror is extreme, interestingly, it is Montresor himself who experiences the ultimate terror.
Indeed, Montresor experiences not only the terror of Fortunato--"Yes...for the love of God"--, but he also feels the terror of his deed. Thus, in "The Cask of Amontillado," it is not the preternatural experience of the niter-covered catacombs, nor the call of Fortunato that disturbs Montesor even though he complains of his impatience and the dampness. Instead, his "heart grew sick" because of his comprehension of his terrible deed. Like Kurtz of Joseph Conrad's Heart of Darkness, Montesor could well utter the words, "Oh,the horror! the horror!" in his realization of what he himself has been capable.
At the end of the story The Cask of Amontillado, by Edgar Allan Poe, we find Montressor and Fortunato inside the former's (Montressor's) catacombs in a quest for a cask of Amontillado wine, which is quite precious and is one of the very rich possessions of Montressor. This wine is meant as bait for Fortunato--a man who enjoys his drink--since Montressor is planning his horrid murder. Therefore, Montressor wants Fortunato to be drunk with wine so that he can bury Fortunato alive within the catacombs.
What strikes the reader the most is that Montressor, as he narrates his actions, still has the gall to call Fortunato his "friend," even as he builds the walls within which he is to trap Fortunato alive. The last time Montressor calls Fortunato his "friend" is the moment when he leads Fortunato straight to the "bait," which was the wine.
[MONTRESSOR]: The Amontillado!” ejaculated my friend [Fortunato], not yet recovered from his astonishment.
Soon after this incident, the deed begins to take place, and we see the coldness with which Montressor continues to narrate his actions. This is the part that is shocking and morbid, even sadistic, to the average person.
[MONTRESSOR]: My heart grew sick; it was the dampness of the catacombs that made it so. I hastened to make an end of my labour. I forced the last stone into its position; I plastered it up. Against the new masonry I re-erected the old rampart of bones. For the half of a century no mortal has disturbed them. In pace requiescat!
Here we see more sadistic behavior. He is unmoved by his crime. He blames the dampness of the catacomb for the "sickness" of his heart. He hurries up to finish his work and ensures that it is done correctly. In a more sociopathic twist, he even offers his respects to what will be Fortumato's remains and wishes that the man may rest in peace. What this shows is a disturbed, confused, and sick mind that finds pleasure in his task. Nothing more than the behavior of a sociopath and psychologically deranged man.