Although the English writer Siobhan Dowd did not start writing novels until her 40s, she proved to be quite prolific – completing four novels in a few years, beginning with A Swift Pure Cry, published in 2007. She also wrote a detailed outline for a fifth novel about a boy, his mother, cancer, and the healing powers of a tree, the Pacific yew, the bark of which is used in the manufacture of Tamoxifen, a drug used to treat breast cancer.

That manuscript was not finished when Dowd died of breast cancer at age 47 in August 2007, but it had been acquired – Walker Books publisher Denise Johnstone-Burt had given Dowd a contract for it on the basis of the outline and a few thousand words of prose. Johnstone-Burt, who met Dowd when she bid (unsuccessfully) for A Swift Pure Cry (won at auction by David Fickling Books), was determined to get the book she did acquire finished. She turned to a new star in her stable: Patrick Ness, author of the Chaos Walking series, who had never met Dowd, but knew her name well.

“We were always up for the same prizes,” Ness said. Both writers had novels on the Carnegie Medal shortlist in 2009 (Dowd won, posthumously, for Bog Child); both were finalists for the 2008 Guardian's Children's Fiction Prize (Ness won for The Knife of Never Letting Go).

Would Ness, Johnstone-Burt wanted to know, consider finishing Dowd’s last novel?

"Normally, it wouldn't be anything I would consider doing, because I need to write freely and if I tried to mimic someone else, I think I'd write a bad book," Ness says. "But the idea was so good, I started getting my own ideas about how I would write the story."

Titled A Monster Calls, the Dowd-Ness collaboration is slated for publication in May 2011; Candlewick is the U.S. publisher. Ness says he's glad he overcame his initial reservations and signed on: "The whole situation is so exciting. It's like being handed a baton and told to finish the race. I've taken the baton from a really great writer. I want most of all to write a book Siobhan would like."