Fortunato, a wine expert, did something to make his Mosntresor want revenge on him. HE encounters him at the carnival celebration and tells him about his Amontilliado, a very expensive wine.
Montresor wants revenge on Fortunato, so he takes him down to the catacombs where he takes him down to the catacombs where he keeps all of his alcohol. He plans to show him his amontillado.
They approach the niche when the Amontillado supposedly is. Montresor suggests that they go back because the niter is bad for their health, and that Luchesi, another wine expert, can see it. Fortunato goes in anyways.
About 50 years ago..
Montresor chains Fortunato to the wall of the niche and stabs him.
Montresor builds a brick wall over the niche so it looks like nothing even happened. He is satisfied with his revenge.
50 years later, Montresor finally tells the story about how he got revenge on Fortunado by locking him in the hole in the catacombs and how he was finally content.