The Silent Appeal (by Janice Hallett)

The sequel to Hallett's novel The Appeal, also an epistolary-style murder mystery told through texts, letters, emails, etc.  About an amateur drama group (the same one covered in The Appeal although I remembered almost nothing from that book). 

Thoroughly enjoyable. She's great at vivid characterization and the book was very fair play, even though I didn't guess the ending. So far the solution in The Killer Question has been my favorite but still an extremely fun read.