There are times when a special acting talent seems to emerge out of practically nowhere. Brie Larson had been around, with a supporting role in the Toni Collette vehicle The United States of Tara, and films like 21 Jump Street, Scott Pilgrim vs. the World and Greenberg. They were good performances all, but around the time of The Spectacular Now in 2013, it started to become clear that there was more to her than supporting roles in comedies. This potential was realized the very same year in Short Term 12, her first true blue starring role, one that she grabbed by the horns and made her own. Many considered it among the best performances of the year, and it heralded her ascent officially into the status of one to watch. After a successful turn in Trainwreck, Larson once again has the opportunity to lead in Lenny Abrahamson’s adaptation of the novel Room.

Larson is Joy, a woman kidnapped as a teenager by Old Nick (Sean Bridgers) and forced to live in a room in a shed in his backyard. Two years into a life of no freedom and constant sexual abuse results in a child, Jack (Jacob Tremblay). The film begins with Jack approaching his fifth birthday, having never left the room (simply referred to as “room” without the need of a definite article) or having any concept of the outside world. Joy, in an attempt to placate the child in such a trying experience, convinces Jack that room is the whole world, and everything beyond it is the realm of the TV (their one connection to culture beyond the walls of their shed). When it becomes known that Old Nick might be losing the home, Joy conspires to break out of room to finally be reunited with her mother (Joan Allen) and father (William H. Macy).

With so much of Room consisting of two people in an aggressively small space, Abrahamson must rely heavily on the strength of his two leads. Larson, despite her young age of 25, is an actress with poise and confidence that defies her youth. Tasked with embodying a woman who is barely that, a girl stolen away from the world before she can reach full maturity and forced to endure years of psychological torture, physical and sexual abuse resulting in a son she loves and must protect despite his existence as a constant reminder of her captor, Larson must do more than her fair share of heavy lifting. Making her a purely sympathetic figure would be an easy and understandable direction in which to go, but Abrahamson and writer Emma Donoghue (the original novelist) take the time to sketch a three dimensional figure, a caring mother who is fiercely protective of her son while simultaneously shattered by her experiences and arrested development. Perseverance is Joy’s key trait, but perseverance is not something easily achieved. If Larson’s work in Short Term 12 caught the eye of cinema fans around the world, Room will certainly catch their attention as well. This time, though, the awards are sure to follow.

She is aided by precocious youngster Tremblay, with long stringy hair that makes others convinced he is a girl. The part Tremblay must play is a difficult one, and he manages to paint a convincing picture of a little boy who truly believes that this tiny shed is the entire world. He is a cipher of sorts, at times more of a representation of Joy’s hopes and fears than his own self, but he is an engaging screen presence who faithfully fulfills his growth toward something quite different from where he started. Equally strong is Joan Allen, who brings a measured blend of maternal warmth and stern frustration in a supporting turn. Donoghue and Abrahamson spin a compelling story, but the cast is what makes it sing.

There are minor aspects to Room that do not entirely work, from the abrupt and not completely explicable character arc for William H. Macy to the mostly workmanlike shot selection that gives the film a generally unremarkable look, but luckily these shortcomings are few and far between. Even more luckily, the most vital aspects of the film, the lives of Joy and Jack, are when it is at its best. It is an uncompromising look at trauma, abuse and neglect and the tenacity and determination required to overcome life’s trials while remaining a steadfast and dependable parent and guardian. This is not the sort of film like All is Lost where literally the entire enterprise is on the back of one actor, but Brie Larson is so fundamental to the story of Room that even when she is not on screen, her presence looms large over the proceedings. Tense, taut and uncompromising, Room is an experience that will not soon be forgotten.