He is old, unfit and shod in yachting shoes, but Harold Fry, retired sales rep, resolves to walk all the way to Northumberland to visit an old colleague, Queenie, who is dying of cancer. The twists and turns of his journey are the backbone of Rachel Joyce's moving debut, The Unlikely Pilgrimage of Harold Fry (Doubleday), praised by Claire Tomalin and set to be Waterstone's April book of the month.

Joyce, 49, a mother-of-four from London who now lives in Gloustershire, has written more than 20 radio plays, and first wrote this story in that format, with her father, who had cancer, in mind. Later she turned it into a novel. "Looking back, doing the book was about trying to keep my dad alive," she says. "The more I thought about an ordinary man doing something extraordinary in a very ordinary way, the more I knew, that's what I want to focus on."

But why does Harold have to walk there? "The point is that he pledges to do something against the odds, in order for her, too, to do something against the odds, because she's dying."