The Wrong Mother by Sophie Hannah

Last year, working mother Sally Thorning spent a week at a hotel with a man named Mark Bretherick. Originally, Sally was supposed to go away on a business trip. But when the trip was cancelled, she decided to take a break from her family and go away. That's where she met Mark. Now, a year later, as she's watching the news one evening with her husband, Nick, she sees a report about a local man named Mark Bretherick whose wife, Geraldine, committed suicide after murdering their six-year-old daughter, Lucy--except the man on the screen looks nothing like the Mark she knew. This is also frightening because her Mark had a wife named Geraldine and a daughter Lucy. Not wanting to get involved, Sally tries to anonymously contact the police with what she knows. Then Sally realizes she's being followed. Is she in danger? Interspersed with Sally's story is that of DC Simon Waterhouse and his old female colleague, Charlie Zailer, who are trying to investigate the deaths. Also included in the novel are Geraldine Bretherick's diary entries. Will the police be able to untangle the personal lives of those involved before serious harm comes to anyone else? Another psychological novel with a maternal bent from author Sophie Hannah. In addition, this is the third book to feature Simon Waterhouse and Charlie Zailer.