A loss of focus turns this small English feature from an excellent film into a routine and mediocre one about half-way through, but its opening reels have touches of understated genius about them and it is full of undeniably moving moments.
It's the dramatic debut for director Morgan, an acclaimedmaker of TV documentaries, who based it on his 2007 Spellbound-style doco Beautiful Young Minds, which followed the British team as it prepared for and took part in the International Mathematical Olympiad.
The beautiful young mind he follows here is that of Nathan Ellis (Baker-Close and later Butterfield), an autistic youngster who lives with his widowed mum Julie (Hawkins) in suburban Yorkshire.
Nathan's preternatural talent for maths comes to the attention of his teachers and he starts taking private lessons from a teacher called Humphreys (Spall), whose encroaching multiple sclerosis lends him just the right blend of sardonic worldliness and existential angst.
Their aim is to get Nathan into the national Maths Olympic team and about the only thing the film doesn't do wrong in its second hour is that it avoids the hackneyed triumphal ending.
It's in that second half that the weaknesses appear in the script, by James Graham, an experienced playwright but screen debutant. Apart from the distractingly meaningless title, it feels a draft or two short of screen readiness as it runs up and down narrative side streets without lingering satisfyingly in any of them. The progress of Humphreys' disease; the promise of a romance between him and Julie; Nathan's friendship with a Chinese classmate; the mathematical basis of Bach's piano music; it all gets a bit dizzying.
The early scenes, driven by Spall's deliciously dry, self-mocking turn, work wonderfully, and the wonderful Hawkins reminds us throughout how fearless she is in close-up, how nakedly ready to give us direct access to her characters' inner lives.
But when Nathan and the team head for Taipei, it separates him from his teacher and his mother and much of the life drains from the film. It becomes clumsily expository, like a documentary of a school trip.
It also, incidentally, presents a pretty sanitised view of autism: Nathan's eyewatering candour gives us a laugh or two, but except for a scene involving a prime number of prawn balls, he's really just a shy kid. Some may find borderline offensive the implication that a minor dramatic crisis can cure such a debilitating and mysterious disease.
Cast: Asa Butterfield, Sally Hawkins, Rafe Spall, Eddie Marsan, Jo Yang, Martin McCann, Edward Baker-Close Director: Morgan Matthews Running time: 111 mins Rating: M (offensive language) Verdict: Half a great film, half a mediocre one
