Sixth-grader Marsha is an only child. She's thrilled about her parents' plan to adopt a little sister, but when Wendy arrives, Marsha's life is turned upside down. Wendy is developmentally delayed, acting much younger than her eight years. She has tantrums, messes with Marsha's belongings, steals the affection of the family cat, and embarrasses Marsha everywhere they go. Why should Marsha agree to officially adopting Wendy and having her join their...