When Geraldine Bretherick and her 5-year-old daughter Lucy are found dead in the bathroom of their luxury home, the case divides new DS Charlie Zailer and her DC Simon Waterhouse. Is it a murder-suicide or something even more sinister, and how watertight is the alibi of the apparently distraught husband Mark? Meanwhile, when Sally Thorne, a young working mother with a husband and two small children hears of the deaths, she is deeply shocked. Months before she’d met a man called Mark Bretherick at a hotel and they had a brief but passionate affair. Now, against the advice of her best friend, Esther, Sally feels the need to get in touch with Mark again to offer her sympathy.