1936. Deep in the forests of the Appalachians, in the small town of Troubles Creek, Kentucky, lives nineteen-year-old Cassie Carterthe last surviving member of a rare lineage of blue people. The lonely girl joins the historic Pack Horse project in Kentucky and becomes a librarian. Riding her trusty mule, Cassie navigates slippery river rapids and dangerous mountain trails to deliver books and other printed materials to the poor residents of Kentucky.