Bitter Moon by Alexandra Sokoloff

Female serial killer Cara Linstrom is free from custody.  Against the police's wishes, she was granted bail in San Francisco and quickly disappeared.  FBI Agent Matthew Roarke, who has become obsessed with the woman and her crimes, has taken a leave of absence from the Bureau while he decides if he is done with law enforcement.  Everyone knows her story, how when she was five a terrifying monster of a man broke into her house and killed her entire family.  Only Cara survived and she was scarred for life by his slashing of her throat.  She was known as 'The Miracle Girl' or at least she was until she started taking revenge.

In his quest to understand Cara, Roarke visits places from her childhood.  He goes to the beach town where she stayed for a while, then goes to the small desert town of Las Piedras.  He is drawn there by the call of a bitter police officer who accuses him of letting Cara go free, but he stays as he starts to realize that this town was the place where Cara started her life on the run.  She was sent there by the social services system after spending two years in prison for wounding a social worker and a fifteen year old boy.  There is no talk about what the two males were doing in Cara's room late at night, only that she has been violent.  Las Piedras is supposed to be a new start but Cara finds that evil exists everywhere.

Cara was only in the town for a short while but it was an eventful time.  The social worker she had been imprisoned for fighting is found murdered.  A building is torched.  And two girls die.  One is the survivor of a horrific rape which left her injured and unable to go back into society.  The other is a quiet girl that Cara notices in the high school and who commits suicide.  Is Cara connected to these crimes?

As Roarke investigates he realizes that something more in going on in the quiet little town.  A monster or maybe monsters reside there and evil has stalked the place for many years.  He finds an ally in a elderly nun who has made her life's work helping children who have no other voice.  Can Roarke find the men who are ruining Las Piedras and discover another piece of the jigsaw that is Cara's life?

This is the fourth book in the Roarke/Lindstrom series.  Sokoloff writes a tense narrative, alternating the viewpoint between Matthew and Cara.  Readers get to feel what it was like to be a young teenage Cara and the forces that bent her to the woman she is now.  The author also uses the narrative to highlight a shameful fact of law enforcement.  There are thousands of rape kits with possible DNA matches that were never tested.  They remain on shelves, waiting for someone to have the funds and motivation to solve the crimes they represent.  This book is recommended for mystery readers.