The psychological thriller is centered on the affluent Cairn family which consists of Brad, Abbey and their two children Joshua and Lilly. Joshua is nine years old and is considered a child prodigy who has matured well beyond his age. He is especially fond of his uncle Ned and often plays classical piano pieces for him. His behavior goes from eclectic to strange when his newborn sister is brought home from the hospital.
Arguments erupt in between Abbey who is Jewish and Brad's father who is an Evangelical Christian. To everyone's surprise Joshua declares he wants to become Christian. Throughout the following days, even more bizarre events transpire and Abbey is emotionally breaking down. The family believes that Abbey is just hallucinating and having a hard time with being a new mother again.
As Abbey's psychological problems increase, Brad decides to take time off of work to help Abbey and look after the children. Joshua has decided he wants to bond with his grandmother and asks her to take him and his younger sister to the local museum. During a trip to the museum, Joshua's grandmother meets an untimely death when she tumbles down the stairs as they are leaving.
At home, Brad discovers that Joshua has been entering his sister's bedroom at night and taunting her. Joshua's father shows up just in time to stop Lilly's stroller from following her down the stairs. Brad is convinced even more that Joshua has something to do with all the unfortunate mishaps that are occurring.
As tensions mound, Brad decides that he has to find a way to stop the madness before anyone else gets hurt. He has even introduced Joshua to a psychologist and to his surprise; the psychologist claims that Joshua is being abused. Not knowing what else to do, he enrolls Joshua in a boarding school which sends Joshua over the edge. As everything spirals out of control, it is up to Brad to put an end to it, once and for all.