Title: A knife at the opera
Description: The second in Susannah Stacey's Superintendent Bone mystery series. 
The girls of Haddon House school are performing The Beggar's Opera when "Mrs Trapse" fails to appear at her cue. One of the girls takes her place and brings the house down with her performance, but what brings up the curtain on a new mystery is the discovery of the body of one of the teachers, stabbed in the back.
Superintendent Bone and Inspector Locker set about solving the mystery, with intervals of the continuing story of Bone's home life, his daughter Charlotte, and other well-fleshed-out characters. 
A great "cosy" mystery!
Places: Tunbridge Wells
People: Superintendent Robert Bone (fictional character)
Time periods: 1980s