I loved their book Behind Closed Doors and parts of this were very similar.

At the end, we learn that Tom/John was holding his parents hostage (similar to Behind Closed Doors) and that he's a psychopath with a hair fetish. Okay? Finding that out was not satisfying in the least - it just felt like Paris was trying to add a shocker moment when really it was just a slightly weird discovery.

I also didn't care for any of the characters. The protagonist is whiny and boring (as one of the other characters point out), and her obsession with the murder is primarily just because the dead woman's name is the same as the protagonist's dead sister. That was similar to the hair fetish thing. Okay..so what?

Basically, I thought her motivations were silly, her reaction to things were predictable, and her discoveries about the "case" were so boring.

I wouldn't recommend this if you like thrillers. I think you'll be unsatisfied.