Fans of the late writer Diana Wynne Jones – who died in March 2011 – are in for an unexpected treat. In the summer of 2014, Greenwillow will publish a new title from the acclaimed science fiction and fantasy author. Titled The Islands of Chaldea, the book is a standalone novel unconnected to any of the author’s earlier works. It is also the result of an unusual, asynchronous collaboration between the writer and her younger sister, Ursula Jones.

“Diana started work on the novel in the first half of 2009 and she expected to finish that year, but when she was about a third of the way through… she was diagnosed with cancer,” Jones’s longtime agent, Laura Cecil, recalled in an email.

Jones put the novel aside while she underwent surgery and chemotherapy. “About a year later, when it was decided that it was pointless to continue with the chemo, Diana began to feel better and began writing again,” Cecil said. “She worked steadily until Christmas, but after then her health became much worse. She continued to write almost to the end of her life, in spite of days when she was in considerable pain.”

Because Jones was always reluctant to discuss her work in progress, no one knew how far along she was with the novel and whether there would be enough material to make the work publishable. It was only after her death that Cecil – along with Jones’s husband and one of her sons – had a chance to read the manuscript.

What they discovered was a nearly completed novel, but with one catch: the story had no ending. “[Diana] did not leave any rough ideas as to how it might end, nor did she tell anyone how she thought the story would be concluded,” Cecil said. “It is possible that she did not know precisely herself.”

Diana’s sister Ursula was another of the manuscript’s early readers. She said she found it gripping: “The story galloped along until the moment where she stopped,” Ursula recalled in an e-mail. “It was horribly disappointing and reminded me of how, when we were all three of us children, my sister Isobel and I would beg her to go on reading [from her first novel]. ‘Don’t you understand?’ she’d say. ‘I haven’t written any more yet.’ And we’d just have to go to sleep agog for the next installment.”

Ursula, the youngest of the three Jones sisters, was tapped by the family to finish the story. She was certainly well qualified to take on the challenge. Trained as an actress at the Royal Academy of Dramatic Arts, Ursula performed for many years at the Unicorn Theatre for Children in London. During her time there she began writing plays for children, all 17 of which have been performed in London theaters. She has also written a succession of well-received children’s books and novels, including The Witch’s Children Go to School, which won the inaugural Roald Dahl Funny Prize.

Still, taking up the story’s thread was no easy task. “I tried to work calmly, hunting and hunting the text for clues, but I had awful nightmares for my pains and not much else,” Ursula recalled. “It was like trying to stir an enormously stiff pudding mixture with a slightly disapproving chef standing in the background.”

It took about six months of reading and pondering for Ursula to experience the flash of insight that made it all come together, she said. “When at last I started to write, it came quickly and easily.”

Throughout the process, she found Diana’s presence nearly palpable. “There was a sense of acquiescence and I often felt prodded into changing things around, too – sentences and structures – as if Diana were leaning over my shoulder. “The last sentence was an unbearable second parting from her: it was as if she had died again.”

With the manuscript complete, it was time for Cecil to let Diana’s publishers in on the project. When she phoned Greenwillow v-p and publisher Virginia Duncan with the good news, “It was a jaw-dropping and absolutely wonderful surprise,” Duncan recalled. “I had thought Earwig and the Witch (Greenwillow, 2012) was the last book we would publish.”

“Laura emailed the manuscript just as soon as we hung up,” Duncan said. “She challenged me to see if I could figure out where Diana stopped and Ursula began – and I really could not. It’s a wonderful story.”

For those at Greenwillow – Diana’s U.S. publisher since 1977 – the project is both thrilling and bittersweet. Her longtime proofreader, Phyllis Larkin, has been assigned to the project, and so has the copy editor who worked with her for many years. Brandon Dorman, who has done jacket art for several of her previous books, is working on the new book’s cover now.

Will more of her work make its way into publication in this manner? It’s too early to tell. “We are still working through Diana’s archive,” Cecil said. “Most of the material so far has been early drafts of published material or fragments – sometimes quite long – which suddenly stop,”

While awaiting the release of The Islands of Chaldea, (HarperCollins will simultaneously release it in the U.K.). devotees can reacquaint themselves with Diana Wynne Jones’s backlist titles, many of which are now available in e-book format. And, of course, get to know the work of Ursula – the other writing Jones.