Dark Saturday by Nicci French

Even though she's made a promise to herself to stay away from crime cases, psychotherapist Frieda Klein agrees to meet Hannah Docherty, who was convicted of brutally murdering her stepfather, mother, and younger brother over ten years ago. Committed to a psychiatric hospital, Hannah has spent much of her time in solitary confinement. When Frieda visits her, Hannah is unresponsive, and in bad shape physically. While Frieda isn't sure of Hannah's guilt, she feels compelled to try and help Hannah because of the state she is in. Soon, Frieda is delving into the murder files, rankling the authorities and people close to the deceased. Frieda also worries that Dean Reeve (introduced in the first book in the series, Blue Monday), whom the police have declared dead, is out there keeping tabs on her. In Dark Saturday, French continues the story of Frieda and her circle of family and friends, while leading the reader through a gruesome psychological puzzle. It will be published next month.