Brie Larson and Jacob Tremblay in Room.

A young woman (Brie Larson) and her 5-year-old son, Jack (Jacob Tremblay), are held prisoner in a backyard shed. When Jack manages to escape, resulting in both of them being freed, mother and son must learn to cope with life outside of their prison walls, and reacquaint themselves with their immediate family.

While Larson is excellent in Room, Tremblay is the biggest reason to see this movie. His portrayal of a small boy who has only known one room in his entire life is revelatory; it’s a performance like none other. While Larson has picked up a Golden Globe and a much-deserved Oscar nomination, Tremblay was robbed.

Joan Allen delivers strong work as Jack’s grandma, a woman who is both dealing with the horror that brought him into the world, and loving him from the instant they meet. William H. Macy has a small but memorable part as Jack’s grandpa, a person who can’t get over what happened to his daughter.

Lenny Abrahamson, who made last year’s excellent yet relatively unknown Michael Fassbender comedy Frank, directs. Based on his work with these two films, he’s one of the industry’s most interesting directors.

The movie basically plays out in two parts: the imprisonment, and the aftermath. Larson delivers a performance deserving of the accolades, but it’s Tremblay who makes the biggest mark.

Room is now playing at the Cinémas Palme d’Or (72840 Highway 111, Palm Desert; 760-779-0430).