The Point of Rescue by Sophie Hannah

I really couldn't get into this book, i recently saw a thriller on TV called Case Sensitive that I enjoyed, based on this book, so i got the book out of the library and found it disappointing.

A woman is watching a report on television of the death of a mother and daughter; apparently both had died at the mother's hand. Also on the screen is the surviving member of the family, a widower described as Mark Bretherick. Watching with her husband, the woman, Sally, has to bite back the words that spring to her lips: this man is not Mark Bretherick! How does she know? Because she had enjoyed a brief sexual affair with the real possessor of that name some time before -- an affair (needless to say) she has not revealed to her husband. Sally is forced to hang on to her secret, and she anonymously informs the police that all is not as it appears to be in this case.

Case Sensitive - 2011

Two part crime drama Case Sensitive begins when Detective Sergeant Charlie Zailer and Detective Constable Simon Waterhouse are called in to investigate the shocking deaths of a mother Geraldine Bretherick and her five year old daughter Lucy.
Unsure whether it is murder or suicide Zailer and Waterhouse must examine every angle, including putting husband Mark under close scrutiny. Meanwhile Sally Thorne who previously had an affair with Mark decides to get back in touch with him only to discover that the man she believed to be Mark is someone else entirely!
Good to see a Sophie Hannah adaptation, she pens a nice line in psychological thrillers and there is a nice line in antigonism between Zailer and Waterhouse too.
cast
OLIVIA WILLIAMS as DS Charlie Zailer
DARREN BOYD as DC Simon Waterhouse
AMY BETH HAYES as Sally Thorne
RUPERT GRAVES as Mark Bretherick
TOM GOODMAN-HILL as Steve Harbord
GEOFFREY STREATFIELD as Jonathan Hey

This was based on the book