After fifteen-year-old Kenny Maxwell's family moves into a crumbling Victorian house in 1977, Kenny discovers a mummified baby and a plea for help in the carriage house. When a girl named Luka introduces him to the backward glass, a mirror that allows time travel, Kenny begins using it to try to save the baby. The more he uses the glass, however, the more convinced he becomes that Prince Harming, a supposed urban legend that kidnaps and kills children, is hunting him, and his time is running out.