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
Aslan brings Jill and Eustace to his mountain and commissions them with the quest to find the lost Prince Rilian.
Act II
Jill, Eustace, and Puddleglum journey north, encountering the Lady of the Green Kirtle and the Giants of Harfang.
Act III
Jill, Eustace, and Puddleglum free Rilian from the silver chair and return to Narnia in time for Rilian to receive a blessing from his dying father.