Seann William Scott is a high school guidance counsellor who murders the parents of abused students ... and the school he works at seems to have an abnormally high percentage of abused students. He's married to Mariela Garriga and they have just had their first child.
As you may have noticed (and you definitely would if you watched the film), this film pretty much steals most of the premise of "Dexter", but it's less plausible and less interesting. Since all the murder victims are related to Scott's students, the police are onto him pretty quickly once his victims are discovered (and they are discovered because he's burying them all under the same patch of land). The movie then focuses on whether Garriga will find out and what she will do if she does.
Nothing very interesting. Despite being stolen from a better TV show, the premise here is minimally interesting, and Scott plays his part well, but it pretty rapidly descends into repetition, and it's ferociously uninteresting. It would take a lot to save this in the last act, once the cops are involved, but there's just not enough there.
Dale Dickey shows up as Scott's mother. There's a whole predictable backstory that explains his behavior, and she's involved, but she's ultimately a less interesting version of James Remar. (Not knocking her performance, but there's very little there.)