Case Sensitive

When Geraldine Bretherick and her daughter are found dead in the bath of their luxury home, it appears to be a clear case of murder suicide. But as the case is investigated by DS Zailer (Olivia Williams) and DC Waterhouse (Darren Boyd), Waterhouse begins to suspect that the husband, Mark Bretherick, is not all that he seems.

Ruth Blacksmith has a new boyfriend, Aidan Harper. Ruth is a music teacher and meets Aidan when he comes to the school to tune the pianos, but she learns that he's an extraordinarily talented pianist. She believes that she can unlock Aidan's gift and get him practising again. Aidan asks Ruth to marry him. She accepts. But there are two problems, firstly she is married to someone else, Jason a fellow teacher, and secondly Aidan admits that he in his past he killed someone. In turmoil Ruth asks her gym buddy Detective Sergeant Charlie Zailer how she might "help a friend" to check if her partner was really responsible for a death as he claims. Charlie is suspicious and in the teeth of opposition from her boss Superintendent Proust, starts to investigate Ruth's background. Charlie fears that Ruth may be in danger and goes to her house to check on her husband Jason. Charlie finds him in the bedroom. He has been stabbed to death. Suspicion falls on Ruth's new man Aidan. As Charlie investigates with the help of her prickly junior, DC Simon Waterhouse, she uncovers a story of thwarted dreams and murderous jealousy. She uncovers Ruth's tangled love life, reveals Aidan's dark past and disturbed family life and in a feverish denouement finally unmasks Jason's killer.

Ruth has been arrested for Jason's murder. Zailer tells her that police know Ruth was in Jason's house on the day he died, prompting Ruth to admit that they had sex -- but she claims that he was alive when she left. Later, when releasing Ruth on bail, Zailer tells her that she has been to see Aidan and has told him about Ruth and Jason, and that Aidan has told police that the woman Ruth saw him with is his stepsister, Mary Trelease. As the investigation continues, Ruth and Aidan question whether they really know each other and wonder what other secrets await discovery.