For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Catherine travels to Bath and meets the Tilneys and the Thorpes. She falls for Henry Tilney, but she is pursued by John Thorpe. Isabella Thorpe gets engaged to Catherine's older brother James, but Isabella begins flirting with Captain Tilney shortly after getting engaged.
Act II
Catherine is invited to travel to Northanger Abbey with the Tilneys. Catherine lets her imagination run away from her at the Abbey and ends up embarrassing herself. Things are cleared up, but another crisis arises when she learns that Isabella and James are no longer engaged.
Act III
Catherine is mysteriously expelled from Northanger Abbey by General Tilney. Henry chases after her and proposes. After Henry's sister Eleanor gets married to a wealthy man, the General gives his approval to Henry, who then marries Catherine.