After her father suddenly goes missing, thirteen-year-old Claudia Dalton is left feeling helpless and alone. The police have no leads, no clues as to where he could have gone. He just vanished one night, leaving Claudia and her mother to question everything they thought they knew about him and their family. Claudia is inconsolable, but then she stumbles onto a code in her dad's childhood bedroom; it's a curious first clue that puts her on a treasure hunt that she hopes just might help her discover what happened to her dad and why he left.