When a mysterious new girl named Prunella Davidson joins the Chalet School, her prim and proper ways baffle both students and teachers. As Prunella navigates the lively school environment and forges an unlikely friendship with young Len Maynard, secrets begin to unravel. Meanwhile, preparations are underway for the school's highly anticipated sale event. With a daring rescue, surprising revelations, and plenty of laughter along the way, the indomitable spirit of the Chalet girls shines through.