Kylie Bucknell, a troubled young woman, attempts to steal the safe from an ATM but the police capture her. Due to her history of recidivism, she is sentenced to house arrest for eight months under the care of her mother, Miriam. Kylie does not get along with either her mother or her stepfather, Graeme. A security contractor, Amos, explains that Kylie's ankle monitor will alert the police if she ever leaves the premises of her mother's house. Kylie is further frustrated when Miriam claims the house is haunted. Amos takes Miriam's suggestion of a haunting seriously and promises to return with ghost-hunting equipment. After a series of unexplained experiences, Kylie comes to believe there may truly be a ghost in the house. Graeme reveals that their home was once a halfway house and the site of a horrific murder. They discover evidence of the crime, including an orthodontic retainer. Amos attempts to break into her neighbor's house next but the neighbor says that he is not the killer. He tells the story of a young savant, Eugene, whom he adopted. Eugene is an expert at mechanics and electronics and disappeared a year before the killing. Kylie discovers Eugene's secret hallways in their house. She and Amos converge at the police station, and Amos corroborates her wild stories of a serial killer living in the hidden passageways. Once Dennis reveals that he wears a retainer, Kylie becomes suspicious of him. When she confronts him he attempts to kill Miriam and Kylie. Kylie and Miriam flee into the secret tunnels, where they encounter Eugene. Realizing that their paranormal activity has been Eugene all this time, they realize that he is friendly. Dennis stabs Eugene, knocks out Kylie, and begins to strangle Miriam. Eugene wakes Kylie and hands her a weapon, which she uses to stab Dennis. Eugene throws a switch, and high voltage explodes Dennis' head. Months later, all have recovered and Eugene has seemingly become an accepted member of the household.