The stage adaptation of Mark Haddon's much-loved novel The Curious Incident Of The Dog In The Night-time has been one of the great success stories for the National Theatre (of Britain) in recent years.

Adapted for the theatre by dramatist Simon Stephens, the multiple award-winning show has been a hit in the West End of London and on Broadway. It has even survived the collapse of the ceiling at London's Apollo Theatre in December 2013.

Now the story of psychologically troubled adolescent Christopher Boone is touring throughout the Britain and Ireland, including dates in Edinburgh, Glasgow and Aberdeen. Transposing the tale of the boy - whose adventure begins when he finds a dead dog, seemingly killed with a garden fork - from page to stage was no easy matter, explains the show's director Marianne Elliott.

"I don't think it was clear at all that it was a good idea to adapt it," she says. "We never thought, 'this is a watertight idea.' It was always a bit heart-in-mouth [as we developed the production]. We were constantly asking ourselves, 'does it express how Christopher feels?'"

It's that capacity to reflect in theatrical terms the feelings of a teenager who struggles with the pressures of day-to-day life that is key to the play's success, Elliott suggests. Christopher is usually assumed to be living with an autism spectrum disorder, although Haddon, as his creator, argues that the teenager has no specific condition but is, rather, an "outsider" who struggles with the demands of society.

The trick, in bringing Christopher to the stage, is to create an association between the character and the individual audience member. After all, Elliott says, the problems Christopher has in overcoming his fears and in dealing with the trauma of discovering that he has been told a huge lie about his family history are simply more acute versions of issues each and every one of us face in our own lives.

"Christopher triumphs over adversity," the director comments. "He's incredibly brave, but he manages to plough on through it. We recognise ourselves in him. He highlights the things many of us feel are difficult in life. We find other people difficult. We, perhaps, find train stations difficult. We find people lying to us very inhibiting. He reflects an extreme part of ourselves that I think we all recognise."

All of which makes the casting of Christopher critical to the success of any staging of Elliott's production. The London version is now on its third re-casting of the role. There's another Christopher on Broadway, and now young Chris Ashby (who has appeared in such TV shows as Holby City and Skins) tackles the character on tour.

Although Elliott (an associate director at the National Theatre) is no stranger to blockbuster productions - she was co-director on the box-office smash War Horse - she could have had no way of knowing that The Curious Incident would be such a success on both sides of the Atlantic (a US tour, in addition to the current Broadway production, may be in the offing). It was relief, therefore, to discover on re-reading Haddon's book that she would not be strictly limited when it came to casting the hero.

"The novel never tells us what Christopher looks like," she says. "We're usually invited to perceive him from inside his head. [As a theatre director] it allows you a lot more freedom."

Every time Elliott casts a new Christopher she sees the character being reinvented. Each actor has to find his own way to achieve the same or, at least, similar ends.

"There's no one type that we're looking for, really," the director explains. "The only thing that is uniformly the same is that the actors playing Christopher can't be too heavy, because they have to be carried. Other than that, they are completely different types."

Ashley landed the part for the tour because he ticked all the right boxes. "He has a vulnerability and a very likeable quality. He's also good with both text and emotions. The thing about Christopher [the character] is that he doesn't like emotions. Which doesn't mean he doesn't feel them, he just doesn't know how to articulate them or channel them in the way that other people might. In fact, he's a very emotional creature, really.

"So, an actor playing him has to have all of those qualities, as well as being physically quite expressive. Although the Christopher of the novel probably isn't very physically expressive at all, we need that expressiveness on stage."

Despite the accolades in both London and New York, taking a production such this on tour still fills Elliott with a certain nervousness.

"There's a sense of trepidation, as you're not sure what people in different parts of the country will make of it," she says. "It's been very well-received on tour so far. People have come in bigger numbers even than in London. It's been a real tonic for the actors to be received so warmly and to be met half way by audiences."

Here in Scotland, the land of Robert Louis Stevenson and Ian Rankin, we like a good mystery. Good houses for Elliott's production seem all but assured.

The Curious Incident Of The Dog In The Night-time plays Festival Theatre, Edinburgh, April 28-May 9; King's Theatre, Glasgow, August 18-22; and His Majesty's Theatre, Aberdeen, September 1-5. For full tour details, visit www.curiousonstage.com/tour