In the opening of the film The Stepfather we get a sense of normality as the main actor is introduced and he is acting casually shaving, as we later learn that was just to change identity, preparing himself for what we assume to be a casual day and has a cup of coffee, this comes to an end when we see him being normal, alongside a dead family laying throughout the house.
We also believe this is a momento, a momento is a Murderous/ Action/ Passion thriller, we know this is a monmento just from the opening scene of the dead bodies laying around so we acknowledge there has been a very tragic murder. There is also a lot of False Plateau presented throughout the film as we get the sense something is going to go wrong but is actually fine, like when the stepfather leaves to pick up the kids from school but gets a phonecall saying he doesnt have to, whilst he is on his way the son and his girlfriend begin to look around as they believe there is someting supicious about him. He returns and they are still upstairs we believe they are going to get caught in the wardrobe where they hid, but we see a clip of them back in the swimming pool where they was orignally.
The Stepfather is a mystery thriller as throughtout the film we continue to learn in depth the type of person the stepfather really is. Also he persistenly keeps killing people that intervenes with his plan to kill the family, as we witness him killing the neighbour and the freind of the wife who realises he has identity issues with revealing himself and producing valid documents that proves his identity.