Jane and the Opera Dancer — Sarah J. Waldock

This is the third book about Jane Fairfax, now Mrs Armitage. Jane receives a letter from an old school friend, who is the pensioner of wealthy man, who has the task of turning her patron's chosen bride into a lady. When the said patron is murdered, she turns to Jane and her Bow Street Runner husband, Caleb, in the hopes that they might discreetly find out who killed him. The disparate and friction-filled relationships of those at the house party, and some very interesting correspondence leaves no shortages of suspects.