ROOM ****

ROOM is that rarest of films: an achingly emotional tear-jerker with a deep sense of sincerity and the power to confound expectations.

Based on the best-seller by Emma Donoghue (who also writes the script), it follows a young mother (Brie Larson) who, like any other, does her best to look after and nourish her young son Jack (relative newcomer Jacob Tremblay).

The difference is that she does this in a 10-by-10-foot room in which she has been held captive since before Jack was born.

What unfolds is a deeply harrowing experience, one that’s not always an easy watch and demands that you give yourself over to it completely.

But it’s a tremendously moving, thematically and emotionally powerful one that’s rewarding and enriching on many different levels.

Lenny Abrahamson, whose previous films include the understated Irish drama What Richard Did and oddball music comedy Frank, directs this tale of emotional survival and wide-eyed discovery with grace and an astute sense of how to get new things out of this most limited of screen locations.

This small room is all Jack, the child of the ominously named captor and rapist “Old Nick,” has ever known.

The brilliance of the film is how it skilfully navigates its way from the mother’s perspective, exasperated by her situation while her love only grows for her still developing son, and Jack who believes “Room” is all there is to the world.

Larson is terrific in the very difficult role of Ma, saying as much with pained glances and stifled tears as her understandable outbursts of frustration at their confined situation.

But it’s nine-year-old Tremblay who is the shining star of the piece, belying his age to give quite simply one of the best child performances ever put on-screen, as convincing as he is immensely compelling.

Effortlessly sidestepping the exploitative nature to which the premise could easily have led, Room is a unique film that’s haunting, heartbreaking and utterly uplifting all at once.