The film commences in Ohio, where a young woman, Margaret St. James, manages to escape from her captor's lair, only to be discovered with her right hand severed. She flags down a passing vehicle for assistance, a terrifying start to her ordeal. Meanwhile, in Pennsylvania, a young couple, John Blume and Sarah Blume, are brimming with excitement as they head to the hospital for the birth of their son. However, as Sarah goes into labor, law enforcement in Ohio surrounds the home of Edward Scarka, the man responsible for Margaret's captivity. In a shocking scene, Scarka emerges nude, hands raised but wielding something sinister, leading to a fatal confrontation with police. It is revealed that he was clutching Margaret's severed hand, a gruesome twist to the horror already unfolding. Shortly after, Miles Blume is born under ominous circumstances, with blood present at the scene of Scarka's demise.
As time passes, Miles grows into an eerily calm child, showing unsettling traits such as an inability to cry during vaccinations and a disturbing fascination with violence, evidenced by him crushing a spider and mumbling in Hungarian during sleep. Sarah finds herself increasingly alarmed by her son's behaviors, including heterochromia—having two different colored eyes.
At the age of eight, Miles is watched by a babysitter, Zoe, while John and Sarah enjoy a night out. A seemingly innocent game of Hide and Seek ends in horror when Zoe sustains an injury falling down the stairs under circumstances that Miles claims to not remember. This chaotic environment is the start of terrifying occurrences. Eventually, as Sarah ventures into Miles's bedroom, she overhears him whispering an obscenity before waking up in fright, leading her to suspect something is amiss with her son.
Things spiral further at school when Miles, feeling left out, retaliates violently. This incident prompts a visit to Dr. Elaine Strasser, seeking insights into her son's troubling demeanor. During discussions with Arthur Jacobsen, they explore the possibility that Miles harbors a menacing alternate personality linked to the sinister legacy of Scarka, a notorious serial killer who once terrorized the area and exhibited similar eye characteristics as Miles.
The family dog, Tallulah, mysteriously vanishes, and during a search, Miles makes chilling remarks that hint at darker truths. The situation escalates as the boy's suspicious behavior continues, including placing a camera to spy on his parents. One fateful night, Sarah is haunted by a nightmare where Miles morphs into Scarka. This nightmare reflects the terrifying reality of what is happening within her son.
After discovering Tallulah's fate and realizing a horrific chain of events leading back to Scarka’s past, Sarah becomes desperate to save her family. She engages with Arthur in hopes of liberating Miles from the chilling influence of Scarka. Under hypnosis, the dreadful truth unfolds as Miles's voice transforms, revealing Scarka's threats and intentions. Arthur, alarmed yet committed, tries to help the Blumes confront this terrifying reality.
As chaos escalates, leading to horrifying encounters with the dark side of Miles, Sarah grapples with the reality that Scarka's spirit may never truly leave her son. A desperate attempt to confront the legacy of Scarka leads Sarah into a harrowing showdown with Margaret, the woman who survived Scarka's reign of terror. Miles’s actions culminate in a horrifying attack as he unleashes Scarka's wrath upon her, leading to dire consequences.
In the film's conclusion, as tragedy unfolds, Miles is left to perpetuate Scarka's legacy, now embraced by a new family under the guise of innocence. The chilling final moments expose the truth, as he gazes into a mirror and sees Scarka's reflection staring back, cementing the horror that has taken root within him.
