Set high up on the cliffs in the grounds of a ruined monastery is Blinkton High School. Here resides the enigmatic Inky Stevens - a talented and astute student, better known as "the Great School Detective". Working from his secret break-time hideaway, Inky is approached by an unusual client: the caretaker Fred Varley, who is distraught over the loss of the school keys. Who has stolen them? And what is the thief's motive? Can Inky and his two sidekicks solve the mystery and retrieve the keys before Fred has to confess his negligence to the terrifying headmistress ("The Snake")?