If you missed the book and don't know what the room is in


, what follows may contain more spoilers than you need.


In a 4m-square soundproofed shed, Jack (Tremblay) lives with his mother (Larson) whom he (and, for half the movie, we) know only as Ma. As the film opens, Jack is turning five, though it's been seven years since their captor abducted Ma, then a teenager.

Emma Donoghue adapted her own novel for this screen version, which is a story of two halves: one is about the ordeal and the other, equally fraught, about adjusting to the end of it, which is another kind of imprisonment. But the film's difficulty is that the second half lacks the intense focus of the first.

It's hard for film, more or less by definition a third-person form of narration, to match the interiority of a story told entirely in Jack's voice. But while they are in Room (so named because it, and everything in Jack's small world, is personified), cinematographer Danny Cohen (The Danish Girl) packs oddly framed shots full of movement and uses looming close-ups to conjure a chillingly consistent child's eye-view.

When the action moves to the world outside, this control slips and so does the eerily effective tone as Ma (her name, in a savage twist of irony, turns out to be Joy) adjusts to life among people who have moved on, the film becomes a conventional, even banal, domestic drama.

What started out as a heartstopping story of unconditional love ends as a routine melodrama about a noble battler.

That's not to say the film is without astonishing redeeming qualities, in particular the two central performances: Larson, all frowns and pimples in close-up, allows us to see her constant struggle to maintain the pretence of normality for her son and the scenes in which she tells him what's happening and makes a plan are edge-of-the-seat thrilling.

Tremblay, too, is a revelation, by turns guilelessly charming and darkly enraged. He commands our pity for the damage he's sustained as well as our love for his certainty of surviving it.

Lapses of plausibility aside, it's a moving testament to the indomitability of the human spirit, though it's a pretty unsettling one.

Cast: Brie Larson, Jacob Tremblay, Joan Allen, Sean Bridgers, Tom McCamus, William H. Macy
Director: Lenny Abrahamson
Running time: 118 mins
Rating: M (offensive language)
Verdict: A film of two halves