IT WAS the tallest of self-imposed orders, to finish his late father’s last novel.

But the outcome for Piers Torday was not one book, but two.

Hot off the press from Quercus this month is There May Be A Castle, a moving and very original children’s book that travels the road many an adult fears to tread – investigating the subject of love and loss in the way a child can understand.

It was the journey Piers himself was on following his father Paul’s death in December 2013 and then, not long afterwards, the passing of his step-father, renowned Tynedale landowner and character Tommy Bates.

There May Be A Castle was his means of catharsis as he picked up his father’s unfinished manuscript for The Death of an Owl, he said.

“Finishing dad’s book was something I did for him after he’d gone and There May Be A Castle is my reaction to that,” said Piers.

“People said ‘was it emotional working on his book?’, but no, I just felt very proud to be able to do that for him.

“It was writing this book that was emotional, because that’s where my feelings came out.”

He actually wrote both books at the same time, sitting down to one in the morning and the other in the afternoon. When he hit a knotty patch in one, he would switch to the other to give his subconscious the time to unravel it.

Paul Torday, whose first novel was the international bestseller Salmon Fishing in the Yemen, was diagnosed with cancer soon after it was published in 2007.

Despite the prognosis that he had just months to live, he survived another six years and in that time, wrote a novel a year.

When he died – peacefully at his home in Barrasford, surrounded by his family – the manuscript for his eighth, about an ambitious member of a Parliamentary committee for the protection of endangered species who tries to cover up the fact he accidently killed an owl, lay silently on his hard drive in his study.

In a first-person article Piers wrote for The Guardian earlier this year, he admitted he opened the document with some trepidation: “I began to read, fearing that I would encounter some exposure of him at his weakest and most vulnerable – morphine-fuelled non sequiturs or revelations.

“It was the opposite: the prose was him at his most elegant and thoughtful. I found myself enjoying his writing in a way I hadn’t for a while, savouring a lightness of touch and a wit that recalled Salmon Fishing in the Yemen. I was gripped. And then it stopped, two-thirds of the way through, quite abruptly.”

The knotty problems Piers encountered were often to do with trying to second-guess his father’s intentions, his direction of travel in the book.

But complete it he did. It was published by Orion in April.

Given that There May Be A Castle is the receptacle of his own personal thoughts and feelings, this book for children was, indeed, the tougher call.

Already the published author of a highly-rated trilogy – of which one, The Last Wild, was nominated for both the Waterstones Children’s Book Award and the CILIP Carnegie Medal, and another, The Dark Wild, was anointed the Guardian Children’s Fiction Prize winner in 2014 – he was entering uncharted waters.

Piers said: “There had been my grandparents, of course, but this had been the first time I’d experienced such a close loss in my family and I wanted to explain that for children.

“Not to upset and distress them, though. Quite the contrary, I wanted to give them confidence and hope.

“Children have lots of questions about what happens – where are we going at the end of our lives? But sometimes it’s difficult to discuss these things directly with them.

“So I had this idea to illustrate how the power of imagination can carry you through pretty much anything.”

The book opens with 11-year-old Albert Mallory, known as Mouse to his family, travelling to his grandparents’ house on Christmas Eve with his mother and two sisters. In snow and poor visibility, the car crashes and Mouse is thrown from the car.

When he wakes, he’s not in the world he has known any more. Surrounded by whimsical animals, scary monsters, mysterious wizards and dangerous knights, the boy sets off on his quest to find the castle that represents ... safety? Home?

While writing two books at once seems akin to trying to ride two bikes at once, Piers found it anything but. “They complemented each other really quite well. It was a very creative experience in the end,” he said.