Mark Haddon knew he wasn’t the right person to adapt his own widely loved 2003 novel The Curious Incident of the Dog in the Night-Time for the stage. “I simply can’t see it clearly any more,” he wrote in London’s The Times in 2012. There was a second reason: “Surgeons are quite rightly forbidden from operating on members of their own family. You need to be brutal and you need to be objective.”

The Curious Incident of the Dog in the Night-TimeThe Curious Incident of the Dog in the Night-Time. Photo © Brinkhoff/Mögenburg

Fortunately there was someone Haddon thought would unquestionably be tough enough for the task – prolific British playwright Simon Stephens, author of works with titles like Punk Rock, Pornography and Motortown. Their paths had crossed during a residency at the National Theatre Studio more than a decade ago and they had bonded over music, their children, and being grumpy not-so-old men. A bromance ensued.

“We spent time going to lunch and hanging out and having coffee together and whatnot, and he started reading my plays and was very, very kind about them,” says Stephens, talking volubly to...