Tight-lipped Englishman Alex Hughes (Alan Rickman) arrives in Northern Ontario on his way to meet the woman with whom he had a son. He is bullied by an altogether unconventional but lovable 19 year-old hitch-hiker, Vivienne (Emily Hampshire), who needs a ride to her hometown of Wawa. When the car is hit by a truck on the outskirts of her home town, Vivienne dies instantly. Alex finds himself, for the second time in his life, grieving for someone he never knew.
Shocked and stranded in snowbound Wawa, Alex is drawn to seek out Vivienne's mother, to talk to her in person about the fate of her daughter. He also goes armed with trinkets and children's amusements that Vivienne has picked up along the way for her mother. Alex knocks on the door and comes face to face with Linda Freeman (Sigourney Weaver).
Linda is no ordinary Mother. Alex soon becomes aware that Linda is an adult autistic, albeit a high-functioning one. He becomes increasingly involved in Linda's life and the community to which she feels complete indifference, in large part because of her condition. Linda, in turn, becomes attached--as attached as she is emotionally capable of--to Alex and what he can do for her.
Alex also forms a relationship with Linda's sassy independent neighbor, Maggie (Carrie-Anne Moss), and is the object of scrutiny by the ineffectual local law enforcement officer Clyde (James Allodi), who, aside from being jealous of Alex's relationship with Maggie, believes he's discovered a dark secret in Alex's past.
When Alex finally gets back on the road, he has exorcised his inner demons, and the town he leaves behind has also been transformed. He had been tempted to stay and make more of his relationship with Maggie, but knew that it wouldn't suit either one of them. He must return to his life and holds out a faint hope that Linda and Maggie may become, if not exactly friends, then at least more accepting of each other. As the snow melts, each character's memories remain intact but are changed forever by their experiences with each other.