I have no idea what the title refers to, though I know that blue refers to the police. The author has created some strange villains who do weird things to their victims. One of the main characters is Kay Delaney, who has already had her lover killed and has been tortured herself. A normal human being might decide that this is where she should find another career. Instead, she and her partner, Finn, persevere in the hunt for the truth. This is very graphic, and certainly not for the squeamish.