As adaptations of much-loved fiction go, Simon Stephens' perky and imaginative version of Mark Haddon's cult 2003 novel The Curious Incident of the Dog in the Night-Time, cleverly directed by Marianne Elliott, is an instant classic: autistic boy decides to track down killer of neighbour’s dog and finds his mum in the process. It's a grown-up children's story, with swear words.

Curious Incident

On the way, there's a lot of stuff about mathematics, but most of that is translated into a brilliant light show, and Luke Treadaway's impersonation of Christopher Boone, the boy who knows all the countries and their capital cities, and all prime numbers up to 7507, is a really touching, probably award-winning, performance.

A lot of the book is about writing one, but Stephens cleverly translates this into a strand of the supportive teacher, wonderfully well played by Niamh Cusack, proposing the text as a school play in Chris' home town of Swindon. So the stage, designed by Bunny Christie and lit by Paule Constable, with the audience on four sides, becomes an illuminated playground of diagrams and trigonometry.

Treadaway himself is a fine artist, drawing circles to perfection and compiling his miniature railway track with the intensity of a Suffolk cousin of Mr Bean, imagining the route back to his mother even as Nicola Walker as the errant mum explains her defection to Willesden.

And there’s a beautiful evocation of Christopher’s space dreams in a constellation of lights that are only visible in a theatre, or when the natural skies are completely clear. His imaginary life is as vivid as his sense of dislocation, and Treadaway – the original Albert in Elliott’s NT co-production of War Horse – makes magic of this moment.

Similarly, his adventure on the train journey culminates in that terrifying sequence on the underground, which is here rendered with stage-level lights, a trapdoor and a yawning sense of danger. And his teacher suggests he deconstruct his A-level exam answer in a speech to the audience after the curtain-calls; he does, and it’s dazzling.

This is the second outstanding NT ensemble piece this week (following the return of London Road), and Elliott’s company includes the peerless Niamh Cusack as Christopher’s sounding-board teacher, Una Stubbs as the neighbour who spills the beans about mother “doing sex” with Mr Shears, and Paul Ritter as the uncomprehending father, the expressive, more violent, counterpart of James Hayes’ tongue-tied da in Philadelphia, Here I Come! at the Donmar.