Back in the summer of 1983, I had a few months to spare between finishing my degree at Cambridge and beginning my PhD at Warwick. The only thing I remember about that summer is that I spent much of it writing a novel for children called Fragment of a Glass. It wasn’t a very original piece of work: basically just an imitation of CS Lewis’s Narnia series. Four children staying at their grandparents’ house during the summer holidays find their way into a parallel world and have a number of fantastic adventures there.

A few years ago I dug the manuscript out of storage to see if it was suitable for reading aloud to my own children. I could see that it didn’t work, as a whole, but there were things about it that I liked. I liked the way that (even though it was quite a short book) the children grew up during the course of the narrative: they started out at the age of about eight or nine, and by the end of their story they were in their late teens. It seemed that I’d been trying to capture something about what it was like to grow up, leaving your childhood and your youthful fantasies behind.

The other thing I liked was the central narrative device: the children find a fragment of broken mirror which reflects a world other than the one they are living in. In my original novel I groped towards the possibility of using this as a metaphor for the child’s imagination, but didn’t really develop the idea.

And so I decided to salvage these two aspects of the original book, and weave them into a shorter, more compact story. From the beginning, I knew that I wanted it to be an illustrated book, and I didn’t have to look far before finding the perfect artist as a collaborator: during a visit to Naples I discussed the project with my friend Chiara Coccorese, and she immediately offered to work with me on the story. It was a true collaboration in the sense that she drew some of her pictures even before I had written the relevant section of the text, and so I took my inspiration for those parts of the story directly from her images. You can see a couple of her beautiful illustrations here and here.

The book was published in Italian first of all, and didn’t appear in the UK until the crowdfunding publisher Unbound agreed to take it on in 2017. Much had changed in Britain (and the rest of the world) in the intervening five years, so I re-wrote the second half of the book completely to give it a darker mood. But the story still ends on a note of gentle optimism.