Ever since she and her mother moved to Possum Hollow, eleven-year-old Hadley Patterson has been fascinated - and frightened - by the light on Hogback Hill. Rumor has it that a terrifying old woman, a hunchbacked hag, lives there. And while Hadley lies awake at night, alone in the house because her mother is always working, thoughts of the old woman fill her imagination. Then a new boy arrives in town and becomes Hadley's friend. Soon Josh Carter is also wondering about the hag, and about Angus Tull, the weird man who warns children to stay away from Hogback Hill. But wondering is not enough for Josh - or for Hadley any longer. Together Hadley and Josh embark on an adventure that takes them to the top of Hogback Hill, and beyond.