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
The curtain rises with Jean Louise on a train going home. Ah, to go home! What a fabulous feeling.
But, as she explores her hometown, she starts to learn unexpected things, and she wonders if her home is changing, or if she just didn't notice what it and its residents really stood for. Once Jean Louise witnesses her father, Atticus, endorsing racist beliefs, there's no going back home again, literally and figuratively, until she confronts it. But how will she do it?
Act II
Jean Louise spends a lot of time privately agonizing about her own beliefs, and rationalizing them against those of her father, which seem so different. She searches her past, looking for meaning. When she can't take it anymore, she confronts her father.
Their conflict isn't what she expected, and it's up to her Uncle to smooth things over with his own, um, unique brand of peacekeeping.
Act III
In the final chapter, Jean Louise and her father make up, but we do not know the shape of their relationship after it has suffered so many cracks and been reassembled.