Murder Imperfect by Lesley Cookman
The seventh title in the Libby Sarjeant series finds her distracted from involvement with her local pantomime by her friend Harry, who asks her to help a friend of his who has been receiving threatening letters. At first she believes it to be a simple case of prejudice, but soon Libby uncovers links to particularly nasty crimes in the past, revelations that have catastrophic results.