This might be a generous rating: I confess I didn't read the entire book. You need to know why.
The book grabbed me early on--a trucker goes a little nuts, crosses the median, and hits a car he seems to have targeted, killing the couple inside. It all seems tied to a man just tried and convicted in a tiny Mohave town, a man who serves Satan.
From there the book sort of devolves into a series of gruesome murder descriptions and at least one scene of Satan-worshipping which concludes with a sex orgy. That's where I closed the book.
All along I'd wondered if DP Lyle was a man because so much of the way Sam was described -- a sort of "just between us guys" tone crept through to me with the sexualization of a Satanic ritual and the glorification of two women getting into a boxing ring to hit each other.
I'm all for strong female protagonists, and tend to choose the books I read hoping to always find them (Dana Stabenow's Kate Shugak comes to mind), so I'm not a fan of shrinking wallflowers. Because of some of the phrases Sam used, I even wondered if the book had originally been written with a male main character, then switched to female in a later draft, not quite successfully.
Some odd typos and other details were likewise distracting. A Cherokee woman appears in Sam's office to warn her. I'm no expert in Native American tribes, but Cherokees are generally on the East Coast, and while such a character could certainly be in the Mohave, I would have liked some explanation for it.
And somehow it's hard to imagine a town as tucked away as fictional Mercer's Corner is supposed to be having a Starbucks. Or other businesses. Novelists are known to stretch the truth, and I would have bought into a non-brand-name coffee shop. But Starbucks?
Yep, I take the suspension of disbelief seriously. I want to be sucked in, I want to believe this town and these characters exist someplace. When I get poked and prodded and nudged away from that believe, the book fails for me.