Sixth-grader Cordelia Liu arrives at Shadow School and immediately realizes something about the school is different. Soon she begins seeing ghosts that haunt the halls of the school, and learns her friend Benji can see them too. Along with their friend Agnes, the three go on a quest to unravel the secrets of Shadow School and to free the ghosts trapped there. However, they are going up against a sinister force that wants the ghosts there forever.