An act of foul play
(Book)

"November 1911. Lady Emily Hardcastle is celebrating her birthday by seeing a play at the Duke's Theatre in Bristol with her maid and confidante, the inimitable Flo. Act One is a triumph. Then Act Two opens with a body on stage--a real one. One of the cast has been brutally murdered during the interval. When other matters get in the way of Inspector Sunderland overseeing the case himself, he asks the ever-resourceful Lady H to keep a watchful eye on the suspects--and his police colleagues. Rustling up some cunning disguises of their own, she and Flo are soon in deep cover among the cast and crew, pulling back the curtain on some shocking secrets and rivalries. The problem is, everyone seems to have a motive, and everyone seems to have an alibi...In this locked-room mystery in which nothing is as it seems, the amateur sleuths need to put on the performances of their lives if they're to stand a chance of shining a spotlight on the truth." - amazon.com