* Greg and Rowley's fight: Greg and Rowley have a huge falling out after Rowley accidentally ruins Greg's plan to make money with a "Haunted House" for Halloween. They fight, and Greg ends up ditching Rowley at the haunted house, causing Rowley to be upset.
* Greg realizes the truth: Greg begins to realize that he's been acting selfishly and has not been a good friend to Rowley. He starts to feel guilty and misses Rowley's company.
* Greg's attempt to make amends: Greg tries to make amends with Rowley by getting him a Halloween costume. He also gets into a fight with his older brother, Rodrick, to get back the costume, which he had stolen.
* The climax at the haunted house: Greg goes back to the haunted house to find Rowley. He finds Rowley standing alone and sad.
* Greg and Rowley's reconciliation: Greg apologizes to Rowley, and they finally reconcile. They go back to being friends, and the book ends with them happily trick-or-treating together.
The falling action essentially shows Greg's journey of self-reflection and his realization of the importance of friendship. It leads to a heartwarming conclusion where Greg and Rowley's friendship is restored.