A young woman named Margaret St. James, Brittany Allen, manages to escape from a terrifying ordeal in Ohio, where she was held captive by a man named Edward Scarka, a known serial killer. As she flees her captor, she runs towards the road and flags down a passing motorist for help. When emergency services arrive, they discover her right hand has been severed, a gruesome detail that foreshadows the eerie events to come. Meanwhile, across state lines in Pennsylvania, a couple, Peter Mooney as John and Taylor Schilling as Sarah Bloom, are preparing to welcome their new baby into the world. At the hospital, as Sarah goes into labor, police respond swiftly to the scene of Edward Scarka's death outside his home, where he had surrendered to authorities, raising suspicion and dread. In a chilling twist, Scarka was holding Margaret’s severed hand when he was shot, and shortly after, their son Miles is born, with blood at the same spot where Scarka was killed, hinting at a dark connection between the boy and the serial killer.
As Miles grows, it becomes evident that he's an unusual child—remarkably calm to the point of eeriness, not crying during shots or injuries, and displaying unsettling behaviors like crushing spiders and speaking Hungarian in his sleep. His mother, Sarah, notices that Miles has heterochromia, with eyes of different colors, heightening the sense of him being different from other children. When Miles reaches the age of eight, played by Jackson Robert Scott, strange incidents begin to occur. One evening, while babysitting, Zoe, apart from him, gets hurt after a game of hide-and-seek, even though Miles claims to have no memory of playing. Later, Miles exhibits violent tendencies, grabbing a wrench at school to attack a classmate after being denied a project partner, which prompts Sarah to seek help from a psychologist, Dr. Elaine Strasser, played by Paula Boudreau.
In their sessions, they examine a recording of Miles speaking in Hungarian, which translates into threatening words directed at a woman. Dr. Arthur Jacobsen, portrayed by Colm Feore, explains that the dialect is rare and suggests that Miles may harbor multiple personalities, with one dark personality potentially taking over. His explanation is similar to stories of children remembering past lives, like the case of a boy in India claiming to remember his previous existence. Sarah dismisses these theories, but later, disturbing signs emerge. The family's dog, Tallulah, vanishes, and Miles’ comments about her death and his father's abusive past escalate Sarah’s concern. Miles had secretly placed a camera to spy on them, leading John to confront Sarah, who denies any wrongdoing. Accusations fly, and tensions rise, culminating in John leaving the house after Miles insinuates abuse, further straining the family.
Nightmares and unsettling behavior continue. Sarah finds Miles crying at the end of the hallway, and he briefly transforms into Scarka, grabbing her, though she awakens from the nightmare. Miles later asks to sleep beside her, showing affection while questioning her love for him regardless of his actions. However, dark discoveries once again disturb the household: Sarah finds Tallulah’s body, having been gruesomely murdered in the basement, revealing that Miles’ violent tendencies are rooted in something far more sinister.
Seeking help, Sarah takes Miles to see Arthur for hypnotic therapy, attempting to bring forth the "good" Miles personality. During hypnosis, Miles becomes aggressive, scratching the couch, and threatening Arthur with violence, indicating that Scarka’s malevolent spirit might still be controlling him. Arthur notices Miles has scratched Scarka's name into the furniture, and later, Sarah learns from a video that Scarka was responsible for multiple murders, always keeping a severed hand as a trophy. The facts align eerily—Scarka had heterochromia, died shortly before Miles was born, and seems to have returned to finish his unfulfilled business, which he believes involves Margaret, the woman he kidnapped years earlier.
As Sarah uncovers more, she realizes that Scarka’s unfinished business is tied to Margaret’s survival and her book recounting her harrowing experience. Desperate to stop the evil, Sarah and John plan to hospitalize Miles, but their efforts turn tragic. John, in a moment of love and desperation, tells Miles he’s loved no matter what, only for Miles to violently attack him with scissors, causing a crash that lands John in a coma. With her family fractured, Sarah attempts to end the nightmare once and for all. She visits Margaret, pretending to be inspired by her memoir to gain entry, but the confrontation turns deadly when Miles, embodying Scarka, stabs Margaret repeatedly with a knife, claiming "You never should have run away from me."
In the chaos, Sarah tries to protect Margaret but is ultimately shot by a neighbor during Miles' escape. Scarka, still masquerading as the innocent Miles, feigns innocence and appears to gain the favor of a foster family, with his reflection in the mirror revealing the true, sinister presence—the serial killer’s spirit still lurking beneath the surface. The terrifying revelation leaves viewers with the chilling impression that Miles, or Scarka, has not been defeated, and that his malevolence persists, now nestled in a new environment with even less awareness of his dark origins.
