Anyone who has read the Mark Haddon novel on which this, the latest in the NT Live* series, is based will wonder, as I did, how anyone could imagine turning an unbroken internal monologue into a piece of theatre with a cast of a dozen. The answer, it emerges, is: wonderfully.
The book, the title of which tips a hat to Sherlock Holmes, is narrated entirely by 15-year-old Christopher Boone, who introduces himself to us as "a mathematician with some behavioural difficulties", but who would be more precisely described as on the autism spectrum.
If you don't understand what that means, you'll have a pretty good idea of how it feels after watching this brilliantly conceived and executed adaptation, which takes us thrillingly, sometimes terrifyingly, and often hilariously into Christopher's world.
The way in which it brings his thoughts to theatrical life verges on miraculous and in the process, it creates a rite-of-passage story, about triumph over adversity, that is so much more than meets the eye.
"Real" or "normal" life - where those of us that people on the spectrum call neurotypical spend our time - pitches some pretty tricky stuff at young Christopher. His neighbour's dog is dead, pinned to the lawn with a garden fork; Christopher is under suspicion; his Dad's acting strange; and he has to travel all alone from Wiltshire to Willesden NW10, when he's hardly been beyond the end of the street.
Director Elliott puts a nimble cast through some pretty gruelling paces - Treadaway's Boone is a tour de force of endurance and precision - assisted by an exceptional lighting and sound design that brings to life everything from the zodiac to the Tube. Writer Simon Stephens' script is sparkling and smart, too: the conceit is that Christopher has been persuaded by a teacher to make his diary into a play and a running gag, used sparingly, allows him to rerun the on-stage action, and remind us that it's his story, after all.
A jarringly sentimental moment at the end scarcely distracts from the overall achievement, which mixes drama, pathos, empathy and laugh-out-loud humour into a winning cocktail. Make sure you stay after the curtain call. Superb.
Cast: Luke Treadaway, Niamh Cusack, Nicola Walker, Una Stubbs, Paul Ritter
Director: Marianne Elliott
Running time: 185 mins
Verdict: Miraculous externalising of the most internal of novels
* Productions from Britain's National Theatre are filmed live and shown in selected cinemas. Limited screenings. For details, see nz.rialtodistribution.com/ntlive.html