The central gimmick of Lenny Abrahamson’s Room (B) – of mother and son imprisoned in a secluded shed for many years – peaks early; and after the inevitable escape attempt, there’s nowhere else to go as the plot plumbs the psychological aftermath. Brie Larson and Jacob Tremblay give breakthrough performances as a family forged in trauma, and the close bond they form is a highlight of the film. The heavy-handed symbolism of the early sequences that feel virtually in utero (is the room actually the womb?) versus a wider expanse of the great big world as its own mental prison never gather the intended gravitas. Still, much of the film is gripping, and the performances are fresh and affecting. Once the central duo is expanded to a more established stunt-casting ensemble including Joan Allen and William H. Macy, it just doesn’t get more compelling. The film simply continues to long for the confined spaces and finer acting of the mysterious opening moments.