The Girl From Devil's Lake by JA Jance

 This is part of the Joanna Brady series and it's darker than most of Jance's books. The story alternates chapters between the actions of a long-time serial killer and Sheriff Brady's realization that he is someone she has known for a long time. It is a gripping story but as I say, kind of dark. The lighter plot involves the wedding of Joanna's daughter, who is now also in law enforcement.