Ellie Haskell's good friend, Dorcas Critchley, wants Ellie to turn her detecting skills towards discovering who has stolen the sports cup from the trophy case in the assembly hall of Ellie's old school, St. Roberta's. The trouble is that Ellie would much rather not to return to the very place where she really blotted her copy book by committing an act of great cowardice. But Dorcas (and he headmistress, Mrs. Battle) are afraid that news of the theft will tarnish the school's reputation, and rather hope that Ellie will take on the case and discover who stole the cup before news of the cups becomes public knowledge. Unable to resist Dorcas' entreaties, Ellie soon finds herself back at St. Roberta's, going undercover and emersing herself in boarding school life, sifting through the rumours, trying to figure out of the theft is a case of a prank gone wrong or if something more dire is underfoot...