Naomi Watts stars as child psychologist Mary Portman, living with her eighteen-year-old paralyzed stepson, Stephen, the victim of a car accident that saw Mary's husband perish. Stephen has always been a problem child, something that Mary feels guilty about not being able to solve before choosing to send him away, and now feels even more guilty that she has made a decision to send him away again so that he can get better care and so that she can move on with her life. A cold front brings in a major snowstorm to their town in Maine that has both of them trapped in their home, as Mary begins to have visions of a boy she thinks may be the ghost of a patient of hers who went missing, a troubled foster child Tom. She's not sure if her visions are real or imagined, causing her to doubt herself as things within the home begin to seem increasingly more dangerous.