The Perfect Couple by Brenda Novak
Sam is lured away by the next door neighbors and held prisoner while her mother, Zoe, and various other characters try to find her. The action moves along well, but with no surprises. Colin and Tiffany are not the perfect couple -- they are not even perfect psycho killers. They make one mistake after another as they try to outwit the detectives and others assigned to the abduction investigation. Jonathan Stivers, the PI who donates his time to a victims' organization, is called into the case to help the police. He probably would have been better at detecting had he been less interested in Zoe and she in him. The other characters in the story are not well-developed and are stereotypes of the sadistic psychopath and the abused wife. The actual investigation is never fully explained as the police don't make any headway in finding the girl even though she is right next door. I simply felt in a hurry to get to the conclusion of the story knowing how it would all end.
All in all - not a terribly exciting mystery thriller even with the grisly details.