A novel sparked by the Josef Fritzl abuse case might seem likely to be a miserable read. But Room, by Emma Donoghue, is one of the most heart-warming books I’ve read in a long time.

Like Fritzl’s victim, Donoghue’s protagonist is imprisoned in a room and gives birth to children after being repeatedly raped. The story is told by her five-year-old son Jack, who has never known a different life and accepts as normal his meagre existence with rationed food, a few books and occasional access to television.

It has become a word-of-mouth bestseller, translated into Dutch, Swedish, Italian, Hebrew and South Korean. Now the author is travelling from her home in Canada to visit Woodstock for a paperback launch event hosted by the town’s tiny bookshop.

In an interview with The Oxford Times, Donoghue said the choice of Woodstock was partly a way of marking the importance of independent bookshops. “A lot of them are very passionate about books, and often people buy the book as a result. And Room has been one of those books that’s become a success partly because of word-of-mouth.”

She knows the area because the parents of her partner — Chris Roulston, Professor of Women’s Studies at the University of Western Ontario — live in Bladon. She met Chris at Cambridge, after moving from Ireland at 21 to do a PhD on friendships between men and women in 18th-century literature, and secured a publishing deal while still studying. “I was extremely lucky to get a two-book deal at 22,” she said. “So I never needed to get a job.”

Her previous writing has ranged from retold fairy tales to a play about a vaudeville star, but before Room, her speciality was historical fiction. Slammerkin, a novel inspired by a murder in the Welsh Borders in 1763, was a surprise bestseller after she had initially struggled to find a publisher.

For Room, she found herself trawling the Internet for research instead of browsing dusty archives in university libraries. “I was looking at kidnap cases and children raised in strange ways or abused. There were some traumatic stories — women giving birth alone and in concentration camps. I also read up on clinics and child development.

“The research was very upsetting, especially cases of children locked away in the basement or an attic.”

Her readers realise that awful things are happening in the Room, but Jack’s mother creates a reassuring routine, teaching him to read, playing with him and telling him stories. There is Phys Ed (jumping on the bed and running round the room), and Screaming from the skylight. We know that they are screaming for help, but the child doesn’t. He believes the locked room is the whole world, until one day “Ma” admits there is life outside.

As in Oxford writer Craig Raine’s poem A Martian Sends a Postcard Home, the child narrator gives us a fresh view of the world, and is one reason why the book is so upbeat. The author compiled a library for Ma and Jack (it doesn’t appear in the book) which includes Blake’s line about seeing “a world in a grain of sand/ And a heaven in a wild flower”.

Donoghue’s children were five and 18 months when she was writing Room. She said: “I watched them growing up normally and it was such a relief after all that research. My son is very different to Jack — he’s sociable and witty, whereas Jack is more serious. But they do share a universal five-year-old energy.”

The child narrator allows her to touch on deep, philosophical questions in an accessible way, but she realised the subject needed sensitive handling, and was worried the story would struggle to find a publisher. “It was quite a risky book to take on, because it sounds weird. But my publishers believed that a lot of people who weren’t necessarily very highbrow would like it.”

In the end, she landed a ‘substantial’ advance. “It was great to have a high like this in your early forties when you have experienced both sides of success because you aren’t bowled over by it the way you would be in your twenties. I sold the book in this bidding war just before my 40th birthday, which was wonderful.”

She has a short-story collection out soon, but many readers await her next novel, based on an 1870s San Francisco murder.

Room is published by Picador at £7.99. The author will be at Woodstock Methodist Church on February 8. To book, email info@woodstockbookshop.co.uk.