When she finished reading A Monster Calls on the train to work, American publisher Denise Johnstone-Burt closed the manuscript and tapped out a text to the author: "I've finished it. It's astonishing. I'm crying – and I don't do crying in public!"
Now, with the release of the film of his 2011 novel, Patrick Ness is about to make many more people sob. A Monster Calls tells the story of Conor (Lewis MacDougall), a bullied only child struggling to come to terms with the fact that his single parent mother (Felicity Jones) is terminally ill. In present-day England, his stern grandmother (Sigourney Weaver) is unable to provide much comfort; nor is his father, who lives in America.
Help, of a sort, comes from a surprising source: a monster (Liam Neeson) in the form of an ancient yew tree. This venerable earth spirit visits Conor to tell him disturbing fairy stories in which good does not necessarily prevail.
The book addresses not just bereavement but also the awful fear of loss and the troubling issue of wanting a dying loved one's suffering – and therefore your own – to be over. It suggests that being able to accept that such feelings are normal is the way towards healing.
Both the novel and the film, which features an extraordinary performance from the young Scottish actor MacDougall, who lost his own mother a year before filming, are deeply affecting, but the true story behind them is no less moving.
A Monster Calls should have been the fifth novel of the award-winning children's and young adults' author Siobhan Dowd.
The youngest of four girls born to Irish parents in south London, Dowd read Classics at Oxford, before a career with the writers' charity PEN. At the American branch in New York, she founded the Salman Rushdie Defence Committee, which supported the author while he was in hiding during the 1990s.
Though she and her librarian husband had no children, she doted on her five nieces and nephews and would write them stories to read at Christmas. She missed her extended family, so returned to settle in Oxford.
She had already been diagnosed with breast cancer when she started writing the first of her four novels in 2004 at the age of 44. In May 2007, with A Swift Pure Cry and The London Eye Mystery already published, Waterstones named her as one of 25 "Authors of the Future". Three months later she died.
Her third and fourth novels – Bog Child (which won the prestigious Carnegie Medal) and Solace of the Road – were published posthumously.
Dowd's sister Denise, a retired district nurse, had accompanied her to appointments with her oncologist.
"Siobhan had a generous spirit and a big heart, and she was scatty and funny and fantastically intelligent," she says. After being told there was no further treatment, "Siobhan said: 'I've got something I have to tell you. I'm not leaving you any money.' I just burst out laughing. As if I cared about that."
Instead, Siobhan wanted to channel the proceeds from her writing into a trust that would bring literature to young people in deprived circumstances. "It was so typical of her to be thinking about other people even as she was dying," says Denise.
At the time of her death, she had also started working on a story commissioned by Denise Johnstone-Burt at Walker Books.
"She wrote the opening – about 1500 words – and it was about a boy called Conor who is sad because his mother's ill. He is visited by a sort of earth spirit which is going to tell Conor three stories.
"Siobhan was calling the story Mistress Yew, though I know that wasn't going to be her final title. She was taking a cancer drug derived from yew trees, so there was a very poignant connection.
"However, her illness progressed more rapidly than had been expected. When she died, I gave what she had written to the best writer I know, Patrick Ness."
Ness had just completed his hugely popular Chaos Walking science-fiction trilogy.
"My initial instinct was to decline the project, because I have a real worry about writing stories for the wrong reasons," he says. "I was very worried about writing a tribute or a memorial, mainly because that's not what Siobhan would have done. She was a really clever, mischievous writer and she would have told a story."
However Siobhan's Mistress Yew planted a seed in Ness's fertile imagination.
"I read the material she had left and, although there wasn't a lot of it, it was extremely potent," he says. "I immediately had my first idea. As a writer, that's your dream – when an idea sparks another idea – and it's then your job to chase after them. So I decided to do it."
A Monster Calls, which is dedicated to Siobhan, was published to great acclaim and commercial success and became the only novel to win both the Carnegie Medal and the Greenaway Medal (for illustrator Jim Kay). A share of the royalties goes to the Siobhan Dowd Trust.
The film, realised from Ness' screenplay by Spanish director J.A. Bayona, is certain to scoop yet more awards.
Telegraph, London
A Monster Calls opens in Australian cinemas on March 9.
A Monster Calls
Patrick Ness
Walker Books, $19.99