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
Books 1 and 2: The beginning until Eustacia and Clym get married.
Act II
Books 3 and 4: Eustacia and Clym's marriage goes increasingly south, Mrs. Yeobright dies in the novel's climax, and Clym and Eustacia part after a huge argument.
Act III
Books 5 and 6: It's the death and marriage section. Half the cast dies tragically, and the rest get endings ranging from OK to happy.