The Step Daddy.

When a seemingly charming stepfather suddenly stabs his wife and stepson, it lights the fuse to a horrifying string of monstrous murders. On the surface, Tim is a thoughtful and mild-mannered family man, but deep within him lies an insatiable killer, forever on the hunt for his next victim. As his body count rises and his new family begins to suspect the evil he possesses, the race is on to stop this brutal sociopath before he takes another victim.