The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult, I vowed revenge. You, who so well know the nature of my soul, will not suppose, however, that I gave utterance to a threat.

A prelude story implies explaining what happened before the actual beginning of "The Cask of Amontillado" by Edgar Allan Poe. The original story begins with the thousand injuries that Fortunato has done to Montresor.  Finally, the insult to Montresor sends him over the edge.

The prelude might begin when Fortunato and Montresor were children in school together in Italy.  Fortunato was been a bully who teased and taunted Montresor because he was a short, fat boy. Fortunato tripped  Montresor causing him to fall down; then, Fortunato encouraged all of the other children to laugh at him. Montresor's fall caused him to break his ankle.  After the ankle heals, Montresor has a permanent limp.

As they grow older, Montresor has a girl friend named Lucia. With Montresor knowing it,  Fortunato gives Lucia a beautiful necklace and asks her to go with him to a ball or party.  The pair hope to keep Montresor from knowing about them going to the party; however, he happens to see them together and becomes so upset that he throws up in front of Lucia. Lucia never speaks to Montresor again.

When Montresor is eighteen, he decides to buy a vineyard to raise his own grapes and make his own wine.  He talks to the owner of the vineyard and tells him that he will come the next day and bring him his money.  Fortunato finds out that Montresor is going to buy the land.  Hurrying to talk to the landowner, Fortunato brings him more money than Montresor offered and pays the man in cash. Montresor discovers that the land has been taken from him by his old enemy Fortunato. 

Montresor begins to plan the demise of Fortunato.  He starts by courting Fortunato's younger sister Maria; eventually, he marries her. This does not please Fortunato. He believes that his family is superior to Montresor's family.  To make Fortunato believe  that Montresor wants to be a part of Fortunato's family, when Montresor's first son is born, he and his wife name him Fortunato.  Fortunato is pleased by this gesture.

However, this does not prevent Fortunato from insulting Montresor.  There was a meeting of the local wine makers.  Fortunato and Montresor both attend.  One of the other connoisseurs of wine nominate Montresor to be the head of the local group.  Fortunato stands up in front of the group and tells them that Montresor is not capable of choosing the best wines because his palate is not as good as Fortunato's taste buds.  Finally, Fortunato has gone too far.  This insult will cause his own death. 

Montresor will gain his revenge but with impunity.