A young teenage girl, Katie, cannot snap out of her depression after losing her mother. Katie has lost interest in school, her friends, and gymnastics. All that changes in the summer, when she is asked to monkey sit Gibby, her science teacher's Capuchin monkey. Taking care of the monkey changes her life in a big way. Gibby's happy-go-lucky personality renews Katie's zest for life. Gibby helps her with gymnastics, renewing friendships (including finding a potential boyfriend) and overcoming her nemesis, a mean girl who is out to beat Katie at everything.