In the short story, "The Cask of Amontillado," the reader is never told what becomes of Montresor after he completes his plot against Fortunato. Write to tell what happened after the story ends in "The Cask of Amontillado."
I had to do something like this, and put that years later someone was wandering the catacombs (after the wall he walled fortunato up with started to crumble) Fortunato's body was found and montressor confessed.