When you sneak out of bounds, that's when the adventure begins. Something is happening in the old house behind the school in Mirrabooka. Strangers have moved in, a mysterious light appears in the tower at night, and someone - or something - is keeping watch. When Minty and Billie investigate, they find themselves drawn into a one-hundred-year-old mystery surrounding the town's ghostly past and a search for lost treasure. They must decide if it's okay to break school rules to save their friendship. With the threat of another visit to the detention dungeon or even expulsion...how far will they go?