In this book, the police and medical examiner are chasing a killer who violently dismembers his victims. Along the way they meet members of "The Mephisto Foundation," who have strange views about how to define the personification of evil, but who think they can help the police all the same.
You're left under no illusions who the killer probably is pretty early on, so the question posed by the book probably isn't "whodunit?" but more "is there more than one way to define mad?"
Personally I felt that the question left me cold. I didn't really care what happened to members of the police, medical examiners staff or foundation. Don't get me wrong I don't mind answering existential questions, but I only mind answering them when I care about the answer, and I didn't care here.