As a child, the novelist Patrick Gale often heard stories of his mother’s ‘cowboy grandpa’ and his exploits out on the Canadian prairies, but the man was never anything more than an exciting mystery.

As an adult – and a best-selling author with a highly developed imagination – Patrick made the connection between this mysterious figure and the reality of his grandmother’s father having walked out on his family when she was little, and the seeds for his latest novel, A Place Called Winter, were sown.

“It took an unanswered question to set my fictional muscle in motion,” says the 53-year-old author of best-sellers Notes From an Exhibition and Rough Music. “In this case, several questions: Why did he go? How did he survive? Am I anything like him?”

Patrick set about finding out everything he could about his great-grandfather, Harry Cane. Most of the relatives who had known him were now dead, and had resolutely refused to talk about him even when they were alive, but Patrick inherited a “great treasure trove” of letters between his mother and grandmother and discovered his granny’s unfinished, handwritten memoir tucked into one of them.

Not long after marrying and having a daughter, something happened that was never spoken of by the family and Harry was obliged to leave the country, moving to the newly ‘opened’ prairies of the Canadian west, where he began a new life as a homesteader in a town called Winter.

His wife Winnie and their young daughter Phyllis (known as Betty) never joined him, and Betty was raised by her aunts and uncles when Winnie died of breast cancer. She didn’t see her father again until she had children and grandchildren of her own, when he returned to Britain to visit her. Father and daughter weren’t reconciled and Harry returned to Canada, where he remained until his death.

Betty’s memoir still left maddening gaps so Patrick filled them in himself, making the fictional Harry gay, forced abroad by the scandal of an illegal homosexual affair.

“There was no evidence of that whatsoever,” says Patrick, who lives on a farm near Land’s End with his husband, Aidan Hicks, “but as soon as I dared to imagine a secret gay life for Harry, the idea took root and became bewitching precisely because it could so easily have been the case and was so impossible to deny.”

No paperwork survives of Harry’s life, apart from the odd official document, and his family seems to have gone to some lengths to destroy any letters he wrote from Canada. Armed with so little evidence, Patrick set off for Canada where he spent three weeks, visiting Harry’s farm in the prairies and Winter, a now abandoned town, and travelling along the same train lines his great-grandfather would have ridden, which he says was incredibly moving.

On the last day of his trip found a single scrap of evidence of Harry’s life there, after having been unable to find even where he was buried.

“I stumbled on just one paragraph about him in a compilation of local memoirs. Wonderfully, the lady writing – one of his former neighbours – conjured up just the same kind of Harry that I’d already set down on paper, with the best horses in the neighbourhood and lovely table manners!”

Did Patrick have any qualms about using his own family’s history and secrets as material?

“I was a little apprehensive but luckily there are very few surviving relatives who knew Harry or the other men and women mentioned. And, apart from inventing a secret life for poor Harry, I’ve been as faithful as I could to Granny’s version of them all.”

  • Patrick Gale is at Chorleywood Bookshop, Lower Road, Chorleywood, on Thursday, April 30 at 7.30pm. Details: 01923 283566, chilternbookshops.co.uk