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
Sethe and Denver are just about to start a new life with Paul D when Beloved appears on their doorstep. Their house isn't haunted anymore… or is it?
Act II
Things are heating up at 124 and not in a good way. Beloved's become one of the family, while Paul D's slowly getting cast out of the house. Not to mention, Beloved's worked her way into Paul D, if you catch our drift. Things really come to a head, though, when Paul D finds out about Sethe's bloody past and, as a result, leaves. Their split is about as far from a resolution as you can get in the book.
Act III
Little girls grow up. Ghosts are banished. Even people who didn't believe in love learn how to love (and live) again. In other words, it's almost a happy ending. Except, maybe, for Beloved, who may or may not be a spirit in the woods behind 124.