Dekker isn't happy that he and his little sister, Riley, are stuck in Button Hill with their weird old great-aunt Primrose. When he discovers an old clock in the cellar, made entirely of bones and with a skull for a face, he doesn't think much about it. But when Riley goes missing, a strange boy named Cobb appears in Button Hill. He tells Dekker that Button Hill sits on the border between Nightside and Dayside—and that Riley is in Nightside and may never return. In order to save her, Dekker must follow her into the darkness and sacrifice something he thought he couldn't live without.