Jacob Tremblay and Brie Larson in Room (A24)

Even if you’ve read Emma Donoghue’s 2010 novel Room or already heard about this film adaptation, there is little chance that too much foreknowledge will lessen the story’s complexity. At the recent Toronto International Film Festival, it was perhaps the most talked about selection; I couldn’t cover my ears in time before I found out too much about what happens in the film’s second hour. Ultimately, it didn’t matter. One could say that Room is spoiler-proof. It’s not the plot that’s the film’s strength but rather its focus on seemingly mundane daily occurrences, told through the perspective of a five-year-old boy. For Jack, ordinary life-learning moments become revelations, which are magnified given the extraordinary and peculiar circumstances.

The film opens on the boy’s fifth birthday, and the viewer immediately enters into the constrained world of Jack (the remarkable Jacob Tremblay) and his mother, who’s in her mid-twenties, played with alert tenderness by Brie Larson. Right after Jack wakes up, he greets the lamp, the rug, and practically all the objects in his roughly 10’ x 10’ soundproofed panic room–cum–prison cell in which the one door is electronically locked. What’s missing? Scissors, the boy’s hair has never been cut. A skylight provides the only source of natural light, and Jack’s only access to the larger world is through an old TV that picks up Dora the Explorer, as well as the children books Ma reads to him. Every couple of other nights for so, as Jack sleeps in the one closet, a man enters delivering supplies and groceries, rapes his mother, and quietly leaves. One of Ma’s rules: Jack must remain in the wardrobe closet while the man is there.

Lenny Abrahamson directs this intrinsically bleak premise with delicacy. As a result, his actors give vibrant performances. The film is a go-to example of moment-to-moment storytelling and acting. (A rising actor’s director, Abrahamson also made Frank, with an out-there ensemble led by Michael Fassbender.) That Jack is five years old makes all of the difference: he’s still young enough to be curious, with an imagination that runs free.

The occasional sensitive chiming of piano chords is unnecessary; the film works best as a stripped-down chamber drama. Even in the direst moments, the tone doesn’t give in to despair or downplay the horrific scenario. This space has become the only environment that Jack knows, one he was born into. As he has been told by Ma, the goings on of the outside world are make believe; dogs and squirrels frolic only on TV. (Tellingly, one bedtime story that Ma tells Jack is a tale of revenge, The Count of Monte Cristo.)

Viewers become aware of Ma’s resignation through her body language, but in her interactions with Jack, she takes as much delight as her son. Their bond is depicted through play: making his birthday cake and running laps (that is, Jack running from one wall to another). He needs Dora for entertainment, and the audience senses Ma needs her son for her sanity. However, if, according to Jean-Paul Sartre’s No Exit, Hell is other people, then there is more fire and brimstone here when “other people” is a five-year-old. Angry when he doesn’t get his way, Jack lets loose with ear-piercing screams that would be the envy of any soprano.

Initially, the ambience is tensely claustrophobic and unsettling, what with a sometimes shaky camera and the extreme close-ups, not to mention the limitations of the one dark interior location, yet the film strangely opens up. The distance from one part of the room to the other feels off-kilter. Shot in widescreen, the room looks bigger than its actual size. One can imagine how Ma and Jack can compartmentalize such a small space. (Acting students take note: every object or part of the cell has a world defining significance.) It’s also recognizably a home: on the wall are height marks of a growing boy.

The script (by Donoghue) and the direction guide the duo through their transitions without force or predetermination; the psychology is not overwritten or vague but a skillful balance. Sentimental moments are well earned and come as a relief. When one occurs late in the film, as Jack finally bonds with another adult, the camera keeps its distance, not milking the moment. Yet the mental damage of the imprisonment underlines the entire film. Even after she is freed, Ma reassures Jack that “It’s still just you and me.” Is she pledging her love or denying that their circumstances have changed, at least inwardly? That she will allow few others into their orbit is heavily suggested.

It’s been several years since a single film has relied to such an extent on a child actor, placing much of the emotional baggage on pint-size shoulders. Abrahamson’s gamble has paid off greatly. Another gifted young actor, Quvenzhané Wallis from Beasts of the Southern Wild, comes to mind, too, but her character shares the screen with razzle-dazzle cinematography, special effect sequences, and a humid, grungy gothic atmosphere. In the bare Room, though, a linear narrative narrowly focuses on Ma and Jack. Tremblay is directed in such a way that the first time Jack discovers a new experience, it’s as though it’s also a first for the actor as well. It’s performance as documentary and will rank as one of the best modern juvenile acting feats, so lacking in self-consciousness that it’s seamless.