Somewhat fittingly, it was after being approached about working on the score for a stage adaptation of Oliver Jeffers’ Lost and Found that Gruff Rhys realised he had two copies of the book at home already. In the intervening years since he’d read it to his kids, the imagery had stuck with the Welsh singer-songwriter and all-round polymath. A world that’s wind-beaten and sea-salt faded, with pastel hued paint peeling from the book’s pages. Idyllic, but weathered too.

‘Musically to me the seafaring side of the book suggested something worn. Then the text is about loneliness and a need for friendship, so I was going for something that was melancholy but sort of euphoric as well somehow,’ he says.

He laughs at this contradiction, but he’s the right musician to achieve this alchemy. As a solo artist, Gruff Rhys’ MO is melodic, world-building pop with surreal lyrics. The kind of music that can capture a mood and then burrow in your brain like a familiar and friendly earworm – always there whether you’re in need of a laugh or cry.

Approaching the score for Lost and Found was unlike his usual process of writing alone at home or shut away in a studio. Gruff went through the script with Director Will Brenton, who made suggestions but never set any restrictions. The task at hand for Gruff? Drawing out the emotions. ‘Will pinpointing how he wants people to feel when they hear the music was really interesting for me. I love new experiences and that was definitely a fun, new way of working,’ he says. And those feelings? ‘I suppose extreme fragility in the face of the elements – a kind of misplaced bravado by the boy, where maybe the penguin who doesn’t say anything at all is the wise one.’

The dynamic is not lost on Gruff. ‘It could be applied to a lot of things.’ He nods before returning to the score: ‘They're alone on a vast ocean, so it’s trying to make music that gives that sense of space and loneliness – a tiny voice singing on top of this massive ocean.’

It’s clear when Gruff talks about the project that translating the rich seafaring imagery from the page into sound has been a delight. Mixing old and new, he reached for his Mellotron keyboard – a multifarious instrument that houses mandolin and accordion sounds recorded on tape in the 1960s. He also worked closely with music producer Luke Abbott, using cutting and sampling methods new to Gruff to recreate the atmospherics of old jazz records.

‘It's been quite exciting just in terms of technology. We wanted to create something that sounded quite old. So we've been fitting music into programs that make it sound like 78 RPM records from the 1950s.’ The most fun part? ‘Creating rhythm tracks out of boat building sounds – using the sounds of sawing and hammering and nails. That was really exciting, using objects the scene suggested instead of drums.’ (A note to parents and carers with any budding musicians out there – we wouldn’t advise trying this at home!)

This playfulness in approach doesn’t only come out when Gruff is writing for the stage, or for younger audiences – in fact, he doesn't like to think of such projects as writing specifically for children. He references the Insatiable, Inflatable Candylion!, a play he made with National Theatre Wales after his second solo record Candylion started to draw in a decidedly younger crowd. ‘On the album, there’s this quite sweet song and this sort of weird thing happened where people started bringing their kids to concerts, but I never wrote it for kids or anything. It wasn’t something I planned.’ he explains. The challenge (albeit a fun one) was always adapting the record for the stage; not adapting it to a younger audience.

When it came to crafting the score for Lost and Found, the approach was no different. ‘I don’t think of it as children’s music... I think kids so often are so sure in their own tastes in music and open to anything – but at the same time really critical – much more honestly critical than adults. So I never try and cater to children in that sense, in case it kind of patronises them.’ Regardless of age, he notes how seeing another world come to life on stage can be a spellbinding experience. ‘It's really amazing to be involved with the show and see this thing grow from the pages of a book into a whole world. Seeing the theatre set develop from drawings into the stage design... totally magic and inspiring,’ he says.

Gruff speaks warmly about working with the creative team; of being one piece of the puzzle bringing this timeless story to life. What does he hope young and old people alike will take away from seeing the show? ‘I think we live in an extremely troubled time of conflict and this is a simple moral tale about the power of friendship. And that hopefully, as part of that storytelling, the music will give people some kind of hope.’

Lost and Found runs from 12 December to 6 January at Aviva Studios. Photography by David Levene.