Many hostage dramas build to a suspenseful point of no return, using a potential escape as a cathartic resolution beyond which little is used to explain or detail the real-world readjustment of any survivors. But it’s after this point that the storyteller’s most difficult task begins in earnest. Emma Donoghue, adapting her own much-read novel for the big screen, achieves an almost perfect separation of within and without perspectives. Instantly we’re immersed in a starkly realised scenario as Joy (Brie Larson) and her son Jack (Jacob Tremblay) are held captive inside a single room by Old Nick (Sean Bridgers), a man we know little about and see only in glimpses, initially, from the perspective of Jack who is made to hide in the room’s cupboard whenever the man enters.

The opening hour of Room (2015) is disconcertingly intense and claustrophobic. In a sense, it becomes hard to downshift away from once the narrative is opened up and a more conventional post-trauma analysis is delved into. Mostly, this is achieved by Donoghue with a degree of believable acuity, and without overturning the distress and complexities of the pair’s return to the real world with emotionally overwrought machinations. A moving though subtle, never pandering score by Stephen Rennicks also helps maintain the film’s emotionally even keel.

A couple of moments do come close to the brink of upsetting the fragile tone but Larson formidably grounds Joy with a credible level of distrust in superficiality as normality when seen through the blunted eyes of a survivor. Tremblay is a marvel too, making a deep impression in what must have been an exceedingly challenging role for such a young actor. There’s a solid support cast led by the ever-staunch Joan Allen as Joy’s distressed and unequipped mother. William H. Macy is sadly neglected however as Joy’s father with his couple of scenes creating a tension between he and his daughter that’s never appropriately addressed and curiously left unresolved.

Room remains resolutely engaging throughout even if its opening hour, despite its limitations, is its strongest. Much of the credit for this can be given to director Lenny Abrahamson. His early Irish films, Garage (2007) and the flawed but fascinating What Richard Did (2012), earned him a much higher profile project with his previous film, the brilliant Frank (2014). The promise of these earlier works is now confirmed with Room, in which he’s able to negotiate a tiny space for an hour and yet never allow the storytelling to become bogged down by an exaggeratedly compressed environment or, later, yearning for a simple understanding of the true notions of freedom and happiness.