The Last Act of All — Aline Templeton

Forbidding and remote, Radnesfield was a village whose inhabitants resented all outsiders. So when soap opera star Neville Fielding moved into the old Radley mansion with his beautiful, aloof wife, Helena, and their horse-mad fifteen-year-old daughter, Stephanie, the villagers closed ranks and turned their backs on their new neighbors. No one could have guessed the storm that would blow their sheltered world apart.
Before long, Neville's inveterate philandering drove Helena to divorce, and then into the gentle arms of the retiring Edward Radley. Neville's grisly death shocked the quiet community, and Helena, caught in a string of lies, confessed to the killing and was sent to prison. But why did she refrain from making the plea that would have softened her sentence?
When Helena returns to Radnesfield after serving time for the murder, Detective Sergeant Frances Howard, fearing for her safety, decides unofficially to reopen the case. Another killing soon confirms the evil lurking in Radnesfield - evil that finally, shockingly, exposes the diseased heart of the society.