The film begins with Mary, a dedicated child psychologist working from home, as she bids farewell to her 18-year-old stepson, Stephen. His father, Richard, is taking him to a special school for the summer, but Stephen's anger is palpable. During their drive, an argument ensues, and Richard reminds him of his expulsion from school, resulting in a tragic car accident when they collide with an oncoming truck.
Fast forward six months, the scene is now blanketed in snow surrounding the home where Mary and Stephen reside. Tragically, Richard was killed in the accident, leaving Stephen paralyzed from the neck down, unable to speak and entirely reliant on Mary for care. Each day, Mary dresses, bathes, and feeds him, while he spends his time in front of the television as she attempts to maintain her practice. Yet beneath the surface, Mary harbors plans to send Stephen away at the end of the month due to the overwhelming burden.
Among her patients is Tom, a little boy who is both hearing-impaired and mute. His social worker, Joan, brings him to see Mary, but despite his aggressive behavior, she believes that she can help him. However, Joan surprises her with the news that this session will be Tom’s last, as he is being moved to a special school in Boston. Concerned for his inadequate winter clothing, Mary gifts him a knitted hat and scarf that once belonged to Stephen.
During a video call with Dr. Wilson, the family physician, Mary confides her struggle with sleep issues, prompting him to order a blood test. Later that night, she hears strange noises outside, only to discover a raccoon. However, her relief is short-lived when she finds Tom hiding in her car after breaking a window to escape. Despite her best efforts to keep him safe, he panics and runs into the freezing woods, prompting Mary to call for the sheriff in a desperate search. Unfortunately, the search yields no results; Tom is presumed dead, either from exposure or having taken his chances far from the area.
As Mary copes with the eerie absence in her home, her nightmares become increasingly haunting, filled with visions of Tom. She wakes one night to find him in her doorway, only for him to vanish moments later. Despite Dr. Wilson's insistence that such visions are manifestations of stress, Mary feels firmly that she sees Tom's ghost. News reports suggest that a boy resembling Tom has been spotted in Florida, which brings her some comfort, though her life remains fraught with tension.
Adding to her stress, a power outage is looming due to an ice storm, prompting her to prepare her home against the elements. Nonetheless, as Dr. Wilson reveals alarming results from her blood tests—showing high levels of medications prescribed for Stephen—concerns about her mental well-being intensify. When Mary attempts to retrieve lanterns from the basement, she has a tense encounter with Doug, the father of one of her patients, who unexpectedly drops by.
In a shocking twist, as the power finally goes out, Mary sees the outline of Stephen in the shadows and screams in terror. She awakens to find herself bound and gagged in the bathtub. With a chilling calm, Stephen reveals that he has been feigning his paralysis, manipulative and controlling, having drugged Mary to maintain his facade while plotting against her. He believes she wants to replace him with Tom, and in his delusion, determines to eliminate the boy who escaped.
Dr. Wilson tries to intervene but tragically meets Stephen’s wrath, just as Mary musters the strength to escape her captivity. After a harrowing struggle, Mary defends herself and Tom from Stephen, ultimately killing him with a hammer.
In a hopeful conclusion, we see Mary and Tom in a car, ready for a new beginning as they drive to a child and family center. Papers await her signature, marking the final step toward adopting Tom, indicating they are leaving the darkness of the past behind to embark on a fresh chapter together.
