A widower and father, Superintendent Bone attends a performance of The Beggar's Opera at his daughter's school. Backstage, someone stabs to death a teacher, Claire Fairlie, and Bone takes charge of the case. The investigation uncovers unsavory facts about the victim, who had been resented by wimpy, ineffectual Miss Wallace, by competitive Miss Lambert and by other staff members. Bone finds many suspects among students whom Fairlie first favored and then ignored, as well as her discarded lovers. Working through a maze of true and false stories, the inspector gathers evidence and identifies the surprising killer.