In April 2006, fifteen-year-old Oliver went hiking to the lookout on Burning Mountain - and vanished without trace. His schoolfriends - Bob, Bell, Phil and Paul - were the last ones to see him on the trek, yet the teenagers were never able to explain his disappearance. Almost twenty years later, Detective Rebecca Giles is called to bushland on nearby Mount Wingen. There a skull has been dug up, reviving the mystery that has haunted the Upper Hunter area for years.