A family, the Walkers, find themselves moving into a new home, to the disgruntlement of teenage daughter Belle (Bella Thorne) having to start her school year all over again rather than picking up where she left off at her previous school. Her mother, Joan (Jennifer Jason Leigh) is unconcerned, reminding her that the move was better for the care of her twin brother James' (Cameron Monaghan) care. Three years ago, James was severely injured in a three-storey fall and left brain-dead as a result; despite James showing no sign of waking in that time, Joan holds on to hope that her son will eventually awaken.
Soon however, as she starts at school, Belle learns that the house they have just moved into is 112 Ocean Avenue, the dreaded Amityville house, and is told of the DeFeo murders that took place there forty years prior and of the film franchise based on the strange happenings that have occurred since. Therefore she is unnerved when unexplained things do begin to happen at home involving her brother, slowly leading her to realise the danger her family is now in.
This film provides examples of:
- Abusive Parents: Joan Walker consistently ignores Belle, blaming her for the incident that left James in a coma. It gets worse by the third act when she attacks Belle for trying to leave the house.
- Her relationship with her second daughter, Juliet, is not much better. She often pressures the little girl into speaking to her comatose brother.
- And I Must Scream: After regaining consciousness, James is fully aware that there is a second presence inside of him that wants control. And because of the damaged state his body is in, there is literally nothing he can do but silently beg for help from his twin sister.
- Anyone Can Die: Out of the six members of the Walker family, including Candice and the dog, only two make it to the end alive.
- Big Sister Instinct:
- In spite of the heartbreak it causes her knowing that her actions will end James' life, Belle accepts her brother's wish to die as himself and pits herself against the spirit possessing him.
- In the third act, when the spirit completely overtakes James and she herself realises her mother is too far gone, Belle's only priority before taking on the spirit again is to save her younger sister, Juliet.
- Bittersweet Ending: Belle manages to save Juliet and defeats the spirit, releasing James from its control. However, Candice and Joan were killed, and James died shortly afterwards. In the epilogue, it's revealed Belle is being questioned by the police in regards to the deaths, with Juliet's version of the events matching up with hers and the evidence resting largely on her side; the only stopping keeping her from being cleared totally is Doctor Milton's testimony that James could not have possibly done any of the murders in the condition the doctor last saw him in.
- Body Horror: James was pushed off a third-floor balcony and left brain-dead for three years, which has caused long-term damage to his body.
- Cassandra Truth: Belle thinks her mother won't believe her when she goes to confront her with the truth about the house. The trope is averted when it turns out Joan knew from the very beginning.
- Chekhov's Gun:
- When Belle and her friends go down into the basement to restore power to the house after a fuse has blown, Joan confronts the three of them with a shotgun, thinking they were intruders. Guess what the possessed James uses in his murder spree.
- The AAC computer James can use with his eyes to speak is used against the spirit later when Belle leaves a message on it that James wants to be taken for a walk. As planned, Joan sees it and happily prepares a wheelchair for her son, leading to an Oh, Crap! moment from the spirit when it realises a walk can take it outside of the magic circle keeping it alive.
- Due to the death of her husband years prior as well as James' accident and resulting coma, Joan has lost all faith in God. In the climax, when she tries to ward off her possessed son with a crucifix, it is a No-Sell.
- Deal with the Devil: At the start of the film, Joan lies to Belle that the primary reason for the move was to be closer to Doctor Milton to make James' care easier for both sides. The real truth is made clear in the third act.
- Disappeared Dad: Belle's father passed away from cancer some time before James' accident.
- Dying as Yourself: Recognising the evil spirit growing in power within his broken body after he regains consciousness, this is what James wants his fate to be. The problem is his mother won't pay attention to his wishes and the spirit won't let him, leaving Belle as his only hope for salvation.
- Evil-Detecting Dog: The Walkers' dog can sense when the evil spirit of the house is rising and knows where the red room is. Which is why the dog is the spirit's first victim.
- Foreshadowing: When Belle implies that her mother's intentions of keeping James alive even though he has shown no signs of life for three years is something that God would not approve of, Joan slaps her in response. This is the first sign the Walker matriarch has lost her religious faith.
- Genre Savvy: One of Belle's new friends, Terrence, is an enthusiast and amateur researcher on 112 Ocean Avenue, having studied the real-life murders and watched the entire film franchise. When Belle informs him of the strange happenings going on, he is quick on the mark to tell her to get her and her family out of the house.
- Hope Spot: When James miraculously wakes up from his coma, it is naturally responded to by his family with joy. Anyone familiar with the Amityville franchise will know this cannot be a good thing.
- Mama Bear: Joan is an antagonistic version of this when it comes to preserving James' life, especially when it's revealed she would do for any price.
- Screw This, I'm Outta Here!: After being affected badly by an apparition the house inflicted on him during an examination of James, Doctor Milton leaves the house, reporting to Joan there's nothing more he can do, and is never seen again for the rest of the film, barring a mention in the epilogue.
- Something Only They Would Say: At the end of the film, its host body injured from its fight with Belle, the spirit tries to lure Belle into thinking James is in back in control and pleads with her to take him back inside the house. Belle comes to realise the ruse, figuring out it just wants to get within reach of the red room and heal itself to continue with the spree.