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
Naomi is a teacher, and life is normal (bratty students and all) until she gets an important phone. This is the message: Uncle is dead. Her Uncle acted as a surrogate father for her, so this is extra-sad. Naomi's father had died and Naomi's mother… well, no one knows what happened to Naomi's mother.
Naomi travels to her aunt, and her old house brings back some pretty unwanted memories. She tries to push them aside, but then Obasan (her Aunt) gives Naomi a huge package. Once she starts reading that, there's no going back.
Act II
We follow Naomi through her childhood in her parents' home, full of happiness and music, to the beginning of World War II. The war changes everything. Her family is ripped apart and forced into exile because they're of Japanese descent.
That's bad enough, but after Naomi is finally comfortable in her new home (you know, the one she was exiled to), the Japanese Canadians are forced to move again (yup, this is exile from exile).
By the end of Naomi's reminiscing, she's no closer to answers then she was when she began. What happened to her mom? She simply resolves to accept not knowing what happened.
Act III
Then something happens. There is a letter from Japan, and it has the answers to all of Naomi's questions. She finally knows what happened to her mother, that she loved her, and why she never heard from her again: she was in Nagasaki when the bomb fell.
The novel ends peacefully. Naomi is calmer than she has ever been. She doesn't feel so lost and confused. The past doesn't have a hold over her.