Knock the door is about an husband and his wife move in an mansion.However,When strange things start going on,Katie,The wife,Thinks that her husband Sam is possessed by an demo
Katie and Sam testabuger move into an mansion.The woman named Ann who is presenting them to the mansion tells them that a man killed his family for unknowen reasons befour killing himself.Katie is freaked out by Ann's behaivour as she runs away after an glass fell down and smashed.
An week later and Katie has moved in an piano.However,When she gets some orange juice,The keys of the paiano start going on themselve,Katie does not know this as an loud car is passing.Sam moves in from his work and says to Katie that his brother is coming with his wife.
Katie is introudeced to Harry and Shannon.Shannon sees an cat and has an strange obession with the cat.She then faints and Harry phones an ambulance.When they get to the phone,An unknowen person walks in and sets Shannon on fire.The others see this and Harry is then sent into an mental asylum.
Katie then investigates the house in the local libary.The libarian named Betty tells her that she stayed there once and was nearly killed by an man with an shotgun.Betty and Katie then find out that the man siad he was Garrison.Katie then learns that Garrison is an demon who possess a man and making him kill his family befour himself.
Meanwhile,Sam is working and his client walks in the office.It is Jim and his wife Fiona.However,Sam then grabs an knife and violently kills Jim.Fiona is stabbed in the leg and crawls out to the hall.Evreyone there is possessed by Garrison and they are watching Sam stalking Fiona.Fiona then escapes but is knocked down by an bus.
Katie then leaves to the house and Betty then sees an little girl looking for an book.She looks for that book but the girl's face turns into Garrison's and this shocks and kills Betty.
Katie comes back to the mansion and finds out that her maid is killed.Katie then sees Sam who is writeing strange symbols in the wall,Not noticeing Katie.
Katie sneaks out and gos to where Harry is.Harry says to her that she must go to hell to kill Sam and Garrison will go away.Katie learns that hell is in the basement of the mansion and she smashes in the door.
Katie is dragged to the well of souls and Katie trys to get back.She is in hell and is nearly burned.However,We see Sam and the man who killed the family.She then looks at the victems and is sick when she sees Betty and Harry who burned alive when she left.Katie grabbed an knife and stabs Sam in the heart.
Katie is then throwen back in the mansion which is quickly getting sapped into hell.Katie holds onto the front door and Garrison grabs onto Katie's leg.Katie kicks him and gets out just befour the Mansion explodes.Katie then collapses and watches the sea nearby,Releaved it is all over.
However,Ann comes back and is possessed by Garrison.An fight occurs and Katie runs on top of an contrusction site.An fight occurs and Katie grabs onto Ann as she is about to fall.Katie makes sure that Garrison dies for good and makes them both fall down into the ground,Which instantley kills them both.
We then see the little girl with her parents,As they are unknowen she is Garrison.Garrison then kills the dad and the mum runs away befour getting dragged in another well of souls