When Ross MacKay was a boy, he loved nothing more than to write. He was not sporty, but give him a blank piece of paper and he was away. He filled a folder with stories set in an imagined world and squirrelled them away beneath his bed where no one would see them. “I never shared them – I don’t even think my parents would know about that,” he says.

Now all grown up and a parent himself, MacKay finds himself forever drawn back to that realm of the imagination. He did it with Tortoise In A Nutshell, the object-theatre company he co-founded after graduating from Edinburgh’s Queen Margaret University, specialising in visual experimentation. He does it in the poetry he writes for young readers, with titles such as Who Put Mums And Dads In Charge? And he did it with his recently published novel, Will And The Whisp, a fantasy about a boy bound to an unearthly spirit.

“I found solace in telling stories, reading stories, watching films,” he says. "What I love about working with young people is their imaginations. One of the workshops I've been doing with kids for Will And The Whisp is making their own fantasy worlds and I love it. The stuff they come up with can be wild, wacky or poetic – their energy is unbound. I love returning to that state."

Treasure Island at Cumbernauld Theatre PIC: Mihaela Bodlovic

He also thinks a lot about the boy he was – a boy not unlike Robbie, the central character in his adaptation of Robert Louis Stevenson’s Treasure Island, now running at Cumbernauld Theatre.

“The play is a love letter to books and stories,” he says. “It's harking back to my childhood. I was the kid that would reach for a dusty book. That was the world I loved."

A collaboration between Cumbernauld Theatre and the children’s company Visible Fictions, Treasure Island is a four-hander in which Robbie summons Stevenson’s characters to life. He imagines himself in the role of Jim Hawkins, the inn-keeper’s son, and dreams up the ship, the buccaneers and Long John Silver, transforming the Forth and Clyde canal into the ocean deep as he does so.

Behind the excitement and adventure lies a moral. After a bad day at school, Robbie has locked himself in his room in order to lose himself in Treasure Island. “He thinks bravery is jumping on a boat, going across the world and beating all the baddies,” says MacKay. "But bravery is more gentle than that. It's about doing things even when you're scared."

Treasure Island at the Lanternhouse, Cumbernauld PIC: Mihaela Bodlovic

It is a valuable lesson for us all and one the writer takes to heart. He remembers himself as an anxious child, an anxiety that, with age, became what he now recognises as a mental illness. Although he adores the camaraderie and creativity of theatremaking – especially the collaborative devising approach taken by Tortoise In A Nutshell – he reached a point when the life of a director, with its unyielding demands and responsibilities, had become unhealthy.

“We were making a show called Ragnarok in Norway and I struggled,” he says. "The daylight was gone, it was a big production and I didn't have the things I could lean on back at home. We were there on a residency but what that meant was I was thinking about the show 24/7. My mental health had been bad before that point and this was the big production I was coming back to. On reflection, that was a bad call. It was too much to take on. The team were really supportive but I knew I had to step away."

After what he describes as a breakdown, he opted to take a sabbatical from the company that had been central to his life for a decade. The break coincided with the pandemic, giving him all the more opportunity for reflection. Needing to create but unwilling to take on the pressures of directing, he found his escape in writing – the very thing he had loved as a boy.

“When I took the pause I started to write again and realised how much I missed that,” he says. "Writing was the thing that was available at home that I could do at my own pace. It was like going back to being a kid."

Sticking a toe in the water last year with The Travelling Cranberries, a half-hour Christmas show performed in the carparks of Fife, he found a job in theatre that was rewarding without being damaging. He took on the writing role and handed the heavy directorial lifting to Jordan Blackwood. "I'm enjoying the change of hats," he says. "You're still storytelling. I don't feel like I've placed Tortoise In A Nutshell down and am doing something completely new. I'm taking that learning with me but doing it in a different way."

It is with Blackwood that he pitched the Stevenson classic to Cumbernauld Theatre. “I've always wanted to do a version of Treasure Island," he says. "It felt like a nice moment – we've had these years of not travelling, so a journey of adventurous escapism, going around the world, felt really appropriate. The world feels scarier than when I was a kid, with climate change, war and the threat of nuclear war, and you can understand why you would feel anxious. I wanted to write something for those kids about what it means to be brave."

Treasure Island, Cumbernauld Theatre at Lanternhouse, until 24 December.

Ross MacKay on Treasure Island: ‘I wanted to write something about what it means to be brave’