It will win you over in the end thanks to a wonderful scene between Asa Butterfield and Sally Hawkins, but the loosely-based-on-a-true-story X+Y makes some questionable decisions in a needlessly overblown second act.


Autistic teenager Nathan (Butterfield, Hugo) is a mathematical genius with hopes of completing the IMO (International Mathematics Olympiad). Mum Julie (Hawkins) does her best to reach her distant son since dad (Martin McCann), the only one who could coax him out of his shell, died. She turns to pothead Humphreys (Spall), a secondary school teacher suffering from the onset of MS, to prep him for the preliminary round in Taipei, Taiwan...


It had the potential to be really engaging and moving but the story makes some ill-advised diversions that threaten to derail the entire enterprise. The biggest snafu is leaving Hawkins and Spall at home, banishing what is a charming and warm love story to a minor subplot. The defence will argue that the story couldn’t justify reasons for mum and teacher to travel to the Far East, but then why does the story have to decamp to Taiwan for two weeks anyway when the actual competition will be held just down the road? Hmm.


Further tidying up could have been attempted in the three-way romance: Once off the plane, Nathan finds he has two suitors (Jo Yang and Alex Davies) but the two girls could easily double up as the same character. As could Spall and Marsan, who becomes Nathan’s teacher and mentor once the story hits Taipei. Moving back and forth between these little stories makes the second act a flabby one.


But thankfully Butterfield guides the film through that shaky middle. He’s got the tough gig – to emote without actually emoting – but thanks to those big saucer-like eyes he isn’t the emotionally cut off kid he could have been and that aforementioned last scene with Hawkins is a heartbreaker. They’re not alone. Spall, Marsan and the underrated Martin McCann turn in dependable performances but it’s the young cast that really excel. Jo Yang, and Alexa Davies are really sweet as the romantic interests, and Alex Lawthor, whose performance as the young Turing in The Imitation Game was bizarrely ignored, is strong again. But it’s Jake Davies, another math student who also turns out to be autistic, that delivers a real eye-catching turn. Even Edward Baker-Close, playing the younger Butterfield in a few brief scenes, stands out.


This cast deserved a better story.