The twins have been reunited, but are definitely not out of danger. Evil Miss Fox may have fled the scene, but headmaster Mr. Bartholomew is back, imposing a reign of terror with his threats of epic punishments should any of the pupils step out of line. When possessions and food start going missing, and the finger of suspicion is pointed firmly at troublemaking Scarlet, she knows she must uncover the truth to clear her name. The twins' investigations through the school in the dead of night reveal a secret hidden deep within the walls, a terrible crime committed many years past, and a very real threat to their present.