Sweet and Sour, by Debbi Michiko Florence

Up until two years ago, Mai and her family has spent every summer with Zach and his family.  That was the year that Zach's family moved to Japan.  It was also the summer that Zach betrayed Mai, hurting her deeply and causing her to swear lifelong enmity for her former best friend.  Now, Zach is back and Mai has to spend another summer with him.  She's sworn to get revenge for his unforgivable cruelty.  However, she finds him changed and her anger and desire for vengeance wavers.  Can she stay the course or will she choose the much harder path of forgiveness?

A sweet middle grade book about friendship and forgiveness, with all of the messy subjects of acknowledging hurt and learning how to let go of negative feelings.  In a vast universe of books about friendships and how to cultivate them, this story has some valuable life lessons to offer and the work that is involved in being a good friend.  I found Mai's stubborn attachment to vengeance a bit arrogant and it made it hard to like her, but she's certainly a good educational example.  The lessons come on a bit too heavy and elements of the story will age poorly, but the kids in the story are relatable and there's a sweet romance and an overall innocence to a story that is hard to find nowadays.