Donoghue’s bestseller drew on the case of Felix Fritzl, who was held captive in a dungeon by his father, and her observations of her own children

I got the notion to write Room in 2008 when I was driving to a book event and mulling over a news story from a few days before about a five-year-old called Felix Fritzl, rescued from the Austrian dungeon where his mother had raised him and his siblings. By the time I parked, and grabbed a napkin to scribble down my thoughts, I knew my novel had to be from the child’s point of view, would begin on his fifth birthday and be split into two halves by the escape, and would be called (in an echo of womb) Room. To tone down some of the horror, and distance Jack’s story from Felix’s, I made him a well-nourished only child, the captor a stranger rather than his ma’s father, their home a locked shed with a skylight and ventilation somewhere in the US.

But the novel really started years earlier, when I gave birth to the first of our two kids. From day one – or middle-of-the-night one, rather – I found child-rearing fascinating. I was a youngest-of-eight who had never had a job that required set hours or responsibility, and motherhood broke and remade me. Only when I got the idea for Room did I realise that I had three and a half years’ worth of things to say. About what a huge gap separates an adult and a small child, with only curiosity, humour and love to bridge it. About how a mother is her baby’s captor and prisoner, sometimes both at the same time. About how you long to give your growing kid freedom while somehow, impossibly, keeping them perfectly safe. Jack’s story was an intensification of every childhood, so I wasn’t writing a crime novel so much as a coming-of-age story in which the growing up had to happen overnight when that door opened. It was also sci-fi, because he’d be an alien among us; and a fairytale that would have to find its way into realism.