Teenager Mandy Winthrop lives with her grandmother, Fran, who runs a private detective agency. In the summer, Mandy works at the agency. When Fran's client, Casualty Insurance, requests an investigation into a kidnapping from a preschool, Mandy's persistent curiosity gets her and her friends into deadly trouble. The arrival of a mysterious stranger, the disappearance of a neighbor, and the Casualty Insurance case intertwine. In her quest for clues, Mandy uncovers a secret about her parents that changes her life. When her grandmother and others involved with the case disappear, Mandy and her friends must act before it's too late.