MARK HADDON once claimed, nay, defiantly trumpeted that his novel, The Curious Incident if the Dog in the Night-Time was “absolutely… un-filmable and un-stageable”. And he certainly had made darn sure no simple man could wangle an adaptation.

“I had grown so tired of novels which were clearly written with a view to selling the film rights that I judged my own writing by its own un-adaptability," he once admitted. Although it did not quite stop him from trying to disprove his own theory and enlist writer Simon Stephens to attempt the impossible.

Seven Olivier Awards and five Tonys later, he has offered his most grovelling mea culpa.

And yet, observing the cast of the upcoming national tour of Curious Incident straining to bring to life protagonist Christopher Boone's thought process in an intensely physical rehearsal in the deepest bowels of the National Theatre, it is clear he may have been onto something.

Arms trembling from the sheer effort of buoying up the lead above their heads before setting him tentatively back down on firm ground (and repeat, until they hit just the right pace, in sync with the ethereal background music), the harried actors would surely agree Haddon made a pretty decent stab at penning a virtually un-representable story.

“Push your arms straight above you and breathe,” urges associate choreographer Jess Williams.

"It will make it easier to keep him up above your head. It’s about Christopher trying to escape; he is overwhelmed by what’s going on around him.”

"One, two, three," the quartet chant in unison as actor Scott Reid, his cheeks flushed and forehead drenched with beads of sweat, tenses every muscle in his body and leaps forward, trusting them to catch him mid-air. This is a crucial scene, 'Astro-Boy' which sees Christopher ‘fly’ into space, offering a rare glimpse into his insulated and skewed perception of reality.

“It should look like ordinary people suddenly lifting somebody above their heads and suddenly this extraordinary thing is happening,” says associate director Elle While, who has taken over directing duties for the tour from original director Marianne Elliott.

“Cup your hands around your eyes,” she corrects Scott, demonstrating with her own. Every gesture down the minutiae of the tilt of his palm or the curve of a finger is flawlessly orchestrated. Any less and the play would be drained of meaning. Incidentally, Astro-Boy has since become Mark Haddon’s favourite sequence.

Later they will tackle the gravity-defying wall-walking stunt, where Christopher races along the set at a 90-degree angle with the help of sturdy actor propping him up below.

Set in Swindon, the National Theatre’s award-winning adaption of Haddon’s novel follows Christopher, a 15-year-old with an exceptional gift for maths but ill-equipped to interpret everyday life.

Although the word Asperger is never uttered it is heavily implied Christopher is on the autistic spectrum. As the play opens his neighbour Mrs Shears’s dog is found dead, speared with a garden fork. Christopher, who is under suspicion, sets out to solve the mystery of Wellington’s murder, recording each fact.

As the teenager struggles to articulate his thoughts, transporting the story to the stage meant turning a topsy-turvy world of muddled words and impressions into firm and, at times, frenzied actions.

This physical take on the book sees Scott and his ‘time-share’ Sam Newton, who will play the part three days a week while on the road, bound, flip, flinch, jerk and run in precisely choreographed routines – with a myriad visual and digital tricks mirroring Christopher's every mood, and rampant confusion.

“Going through that physical experience changes the way you act,” explains Scott, on a lightning-fast lunch break before afternoon rehearsals, this time to run through his lines.

“We all do circuit training together in the morning. We go through that ordeal. The physical stuff and the acting are two sides of the same coin.

"He’s a wonderful boy who sees the world in such an imaginative way. But he can’t lie, and imagine living your life always telling the truth and the amount of trouble that would get you into, that’s Christopher.”

His co-lead agrees: “It’s a challenge. But this is a story we’re telling and this is the language we’re using. We don’t want any labels, this is not a scientific study of autism but this is how his emotions, his world manifests itself. It lets you inside his thoughts.”

And as daunting as the finished ‘dance’ is proving for the dogged actors, both physically and mentally (hence the need for two Christophers to share the role), fine-tuning the youngster's world and projecting his thoughts on stage was nothing short of an assault course for the creative team.

When Simon Stephens sneakily enticed the show’s original director Marianne Elliott to the project - by slipping her a copy of his script under the pretences of picking her brain - she admits she had “no idea how you’d do it, absolutely none.”

What they quickly agreed on, however, was that movement would be key to highlighting Christopher's heightened sense of danger and anxiety in the face of the frantic and alien world around him.

“We came up with some terrible ideas but only stuck with the good ones,” she says. “We thought, actually, if this space is his brain and it’s a box and there are lots of boxes on stage, why don’t we make the stage a proper box with walls and sides - and then we can flip the logic of what is the floor and what is the ceiling. Sometimes when he’s disorientated, he walks along the walls.”

Watching this perfectly crafted, if manic, waltz into an exceptional mind a few hours later in the West End's Gielgud Theatre, where Curious Incident took up residence two years ago, is nothing short of hypnotic.

The seasoned cast have mastered every last jump and step and every piece of this complex puzzle of lightshow, physicality, dialogue and technical gimmicks clicks together in one seamless chasse-croise.

Theatrics aside, Mark Haddon was bowled over by the script, Simon Stephens recalls and his ability to echo Christopher's world view. Especially at a time when, Simon recalls, Haddon “had fallen out of love" with his own novel.

“When he came for a read-through, he had fallen out of love with Curious Incident because that’s all people ever asked him about and nothing else. But by the end of it he had tears in his eyes. He said, 'This is just perfect'," he recalls beaming with pride.

Since its premiere at the National Theatre in 2012, the play has drawn and spoken to the most unlikely of spectators, not least Haddon’s son.

“My nine-year-old son didn’t just enjoy it, he was fascinated by it," he says.

"He likes fighting with sticks and playing football – it’s really hard to glue him down to a seat. Through the whole thing he was completely riveted. Everywhere I go I bump into unexpected people who’ve seen the show.

"The other day somebody came to fix the drainpipes and he told me he’d just seen the show and loved it. I imagined a kind of spectrum with Curious Incident at one end and writeable plays at the other,” he goes on.

“Simon’s genius was to recognise that I was completely and utterly wrong.”

Curious Incident is at the New Theatre Oxford from May 22 to 27. To book go to www.atgtickets.com

A SWINDON STORY

WHILE it has yet to be staged in its birthplace, creator Simon Stephens has always defended Curious Incident as a "Swindon story" first. In the play and even throughout rehearsals, the town became a character in itself.

In fact when the show transferred to Broadway, the American cast were each ordered to get the lay of the land, pour over maps and stockpile as much information about the railway town as humanly possible, if only via the Google search bar - down to the train timetables. One landmark in particular caused quite the stir.

"It was quite funny," smiles associate choreographer Jess Williams.

"They were completely baffled by this Magic Roundabout situation. The presentations were quite interesting; though one girl found this blog called 'Swindon is S***'. But they all took it very seriously. And we do it here in the UK too, we have a research file. It has pictures of every reference to Swindon in the play. We look at road signs, anything that helps paint a picture."

As for the latest crop of thesps due to take the play on its second national tour, the significance of our Wiltshire nook was impressed upon them even before the first read-through.

A couple of them, Emma Beattie and David Michaels - Christopher's mother Judy and father Ed - took it upon themselves to hop on the next available train to Swindon to get to grips not only with the story but with Christopher's insulated world, limited to the confines of his school and terraced house on Randolph Street. Although, as they soon discovered, while the street technically exists, it is in reality named Randolph Close.

They made only one "unsanctioned" detour on their official visit via Pizza Express for sustenance, Emma confesses.

"It was great to get a sense of the architecture and that suburban feel, with rows and rows of the same houses, which makes Christopher feel safe but is a trap for his mother Judy," she says.

"We had a gift of an experience."

Keen to dig a little deeper if only by osmosis into Christopher's autism - a condition heavily implied but never specified in the book or play to avoid labelling - David even planned a stroll past Bath Road's Priory College, a school for students with Asperger's syndrome and associated disorders.

A fortuitous encounter with a parent at the gate, who seeing the pair loitering outside in the battering rain took pity on them, eventually offered them a priceless insight into the plot and their characters' harrowing circumstances, gnawing resentment and internal conflict.

"We were looking at the college from the car park and a mother saw us asked, 'What are you doing?' We told her we were actors doing some research for Curious Incident," explains Emma.

"She said she was picking up her son and told us to come in. We went, 'Is that allowed?' She introduced us to the faculty and they were so generous. We met her son, who in addition to being autistic had learning difficulties, and everyone was totally transparent with us about their experience.

"We asked questions and it opened this gate for us. The school said parents often arrive broken. It's a massive responsibility for them.

"I came out of there skipping. That experience in Swindon allowed us to ask the right questions, we were not going in blind anymore."