Murder In Hindsight by Ann Cleeland

They make a strange couple.  Kathleen Doyle is a sheltered, Irish Catholic girl who joined the police but retained her innocence.  Chief Inspector Michael Sinclair is also Lord Acton, one of England's wealthiest heirs.  They work together on the London police force and when Acton sees Doyle one day, he instantly falls in love with her.  He is actually obsessed with her and quickly convinces her that they must marry.  Now each is famous in their own way.  Acton has long been a darling of the press, his aristocratic background a major story in every situation.  Kathleen becomes a media darling when she jumps from a bridge to save her partner from drowning. 

A new case has come to light.  There is apparently a serial killer at work, one who has gone undetected for a while.  His victims follow no pattern of race, gender, social class or means of execution so there has been no connection.  Doyle, who Acton has put on working cold cases to keep her safe, makes the connection that each of the victims were individuals who had committed a crime themselves and escaped without legal consequence.  There is a vigilante on the loose. 

In the meantime, Acton's actions have made him a target for a shadowy figure.  He has, at times, taken the law into his own hands, and is, in fact, a vigilante who has killed before himself.  Now there is apparently a plot to get back at him and he has plenty of secrets to hide.  Can Doyle solve the murders while discovering how to save her husband?

This novel is the third in the Doyle and Acton series.  The characters are interesting but there are serious flaws in them.  It is hard to engage with a policeman who decides that the laws don't apply to him and who takes the lives of others when he decides it is best.  The worst thing that can be said about the characters is the author's insistence that everyone who meets either of them immediately falls permanently in love with them.  For Doyle, that is her partner, a shadowy figure mixed up in the plot against her husband and of course, her husband.  For Acton, it includes a journalist, a former lover at his ancestral home and every woman who comes in contact with him.  The couple have constant sex, several times daily, and yet constantly question if each other really loves them.  These flaws, if corrected, would make this a more engaging series.  This book is recommended for mystery readers.