Room holds you in a vice for much of its running time, and how could it not? This is the story of a woman (Brie Larson) who has been held captive in a shed for years, long enough to give birth to a now-5-year-old son (Jacob Tremblay) who was fathered by her kidnapper and rapist. It’s an awful scenario, and one that easily stirs up emotions: rage, disgust, fear. I’m not sure the film does much more than take advantage of them, though, in order to make us come out of the movie feeling as if we’ve had a powerful “experience.” Consider the most gripping sequence, an escape attempt by little Jack. Everything that happens is illogical and unbelievable, and not that well-staged by director Lenny Abrahamson (Frank). We are simply emotionally involved because the life of this little boy is in the balance. Still, it’s hard to fault the performances. Tremblay is better when he’s absentmindedly at play than when he’s consciously “performing,” but Larson is a constant wonder. As Ma, she has to communicate desperation and terror to us in the audience while simultaneously putting on a brave face for her son, and we’re with her in almost every moment.