Mary, a child psychologist living in rural New England, grapples with the recent loss of her husband in a car accident that also leaves her stepson Stephen paralyzed and in a vegetative state. Isolated and struggling with the demands of caring for Stephen, she continues her professional duties from home. One day, she starts treating Tom, a troubled young boy, who soon mysteriously vanishes during a severe winter storm. Authorities and search parties find no trace of Tom, leaving Mary consumed with guilt and worry over his disappearance.

As the harsh winter intensifies, Mary begins to experience disturbing phenomena and becomes convinced that an intruder is lurking around her home. Strange sounds and unsettling occurrences escalate her fear and paranoia. Terrifying events mount, and Mary's grip on reality starts to slip. Isolated by the storm and confined by her responsibilities to Stephen, she is thrust into a tense battle against unseen forces, desperate to protect herself and her stepson from an impending threat. The tension culminates as she uncovers shocking truths, setting the stage for a gripping resolution.