"Room" is both accomplishment and conundrum. The film’s first half is so agonizingly difficult to sit through I desperately wished I were anywhere else, while its unexpectedly affecting second half so completely turned me around there was nowhere else I’d rather have been than right in the moment with this singular film.

Adapted by Emma Donoghue from her best-selling novel, shortlisted for the Man Booker Prize for its exceptional literary qualities, the film’s up and down effects are intentional.

The film’s accomplishment is its rare ability to give full weight to both sides of the emotional equation as it tells the story of a young woman imprisoned for years in a single room in a tiny shed and the young son who was born to her there and knows no other world.

Directed by Ireland’s Lenny Abrahamson with uncanny sensitivity and an intuitive sense of what this situation would be like, and transcendentally acted by Brie Larson and Jacob Tremblay, "Room" is several things by turn: creepy, frightening, exhilarating and then frightening and exhilarating all over again.

It puts us absolutely in that dreadful room with those two people, creating a painful and all too plausible nightmare to be experienced by characters Jack and Ma. Could anything be more unnerving than what they go through in that small space? We find out that as well.

One of the keys to "Room’s" success as a novel was author Donoghue’s decision to have it narrated by 5-year-old Jack. Screenwriter Donoghue wisely doesn’t attempt to exactly duplicate that technique in the film, though she periodically uses Jack’s voice-over to ground us in his reality, most effectively in an opening sequence where Jack tells us what he’s learned about his relationship to his mother and his world.

‘ROOM’ Rated R Opens today at Kahala 8

"Once upon a time before I came, you cried and cried and watched TV all day till you became a zombie," Jack matter-of-factly relates. "Then I came in through the skylight, I zoomed down from heaven into Room."

It’s not a room, or the room, but always Room, because the film is always aware that to young Jack, alive and curious as 5-year-olds inevitably are, this 10-foot-by-10-foot space is his entire universe, filled with things strange and curious. As director Abrahamson wrote in a letter to Donoghue, Room to Jack is "a fantastically rich, story-filled and ritualized space."

To Ma, his mother, Room is something else, a torture chamber whose psychological contours we can immediately sense though we aren’t specifically told details just yet. It’s the space where, for seven of her 24 years, she has been the prisoner and sexual chattel of the violent and short-tempered man she and Jack refer to as Old Nick (Sean Bridgers).

Jack has just turned 5, and quite proud of the fact, on the day "Room" opens. He is getting just old enough to attempt to figure out to the best of his ability the space he’s in, to make sense, for instance, of why he’s confined to the wardrobe when Old Nick unlocks the door and enters the room.

Ma, for her part, feels fanatically protective toward Jack, especially where Old Nick is concerned, and, fearful that things can’t go on the way they’ve been, decides to fill Jack in about the nature of the world outside Room. ("No way," he gasps. "Where do they all fit?") Ma also ponders the nature of the options she and her son have, and whether those options have unforeseen dangers and risks worth taking.

Larson has done exceptional work before (she shot to prominence with her starring role in 2013’s "Short Term 12"), but the way she has taken the deepest of dives into this complex, difficult material is little short of astonishing. The reality and preternatural commitment she brings to Ma is piercingly honest from start to finish, as scaldingly emotional a performance as anyone could wish for.

Just as difficult to cast, if not more so, is the role of Jack. As Abrahamson says in the press notes, this is not a part where a child could be himself. "This is a role that needs a proper actor." Young Tremblay (he was 8 during filming) displays a naturalness that is something to behold, and he’s able to hold the screen with just his presence when the situation demands it.

Orchestrating all this impeccably is Abrahamson, an Irish independent filmmaker whose offbeat "Frank," about a man never seen without a huge fiberglass head, does not make him the safe mainstream choice to shepherd a major best-seller to the screen.

But what Abrahamson brings to the table is a delicate touch, a gift for psychological mood and an empathy for altered realities, all of which allow him to get the full measure of this film’s wide-ranging emotions. He and his exceptional collaborators turn "Room" from the film no one wants to see to the one everyone will have to experience.

Review by Kenneth Turan, Los Angeles Times