Eleven-year-old Sonia Molosky's quiet summer and that of her close friends begins to shift after an insurance investigator arrives in Mosquito Creek to settle the vast estate of a young heiress who disappeared seven years before. When Sonia discovers the contents of a suitcase behind a hidden door at the back of her mother's closet, she convinces six of her pals to help her search for new clues to the unsolved mystery. Curiosity soon escalates events to an unexpected discovery that challenges their untested resourcefulness and courage in order to outwit and expose a cruel and cunning foe. While attempting to retrace the path the missing girl rode her horse the afternoon she disappeared, history begins to repeat itself...