Despite Penelope's objections, her parents hustle her off to Tiffin Preparatory School, operated in the old Windorf Hotel. According to the rumors, secret passages and hidden rooms honeycomb the place. There's talk about hidden treasure and may even be a ghost. The first day at a new school never goes well, and for Penelope it is a disaster. Within minutes of being at the school, a teacher falls over dead and everyone thinks Penelope caused it. Soon they learn that the teacher had been poisoned. Penelope enlists the help of her offbeat friends and a quirky professor to find the killer in an adventure that leads across roof tops, through hidden passages and in the woods outside the school. Complications arise when a feud develops with some other students and when the wily principal plots ways to expel her. Before it's over she must save herself and everyone in the school from the hands of a crazy killer and find the ghost's treasure.