Realising there were wild orchids everywhere, the couple snapped photos of every one they spotted on their walk. 'The problem was that, when the prints were developed and we sat down to identify what we had, we couldn't remember where we'd found them. And habitat is an important clue to identification. But we did know the sequence of the photos, which helped us to reconstruct the locations. There was also a pigeon house in one photo that served as a marker.

'It occurred to me that this could be the plot of a great murder mystery.'

Wan, 61, began writing Deadly Slipper with no expectation of being published. She had a full-time job as a research consultant for a drug addiction programme in Guelph, Ontario, her home for the past 30 years.

'But I've been a scribbler all my life, and I thought, 'I want to write something that I'd enjoy reading'. It wasn't easy because, once I started, it meant getting up two or three hours early for three years to squeeze in a bit of writing before going off to work. Sheer determination got me through.'

It's not the first time Wan has prevailed against the odds. She was born during an air raid. 'When the Japanese were bombing Kunming during the second world war, my mother was on the operating table. The medical team attending her had to leave because of the air raid sirens. When they came back after the all-clear, there I was.'

With her mother, her brother and sister, Wan soon left China for India. Five years later, the family headed for the US. Her mother and her maternal grandfather, whose parents were from Fujian, had both been born in the US.

Wan's parents met on a ship travelling to China. She was heading for university in Nanking; he had just graduated from the San Antonio Air Force Academy and was returning home to his Beijing banking family. 'It was a shipboard romance,' Wan says. 'My father joined the nationalist government air force, acting as a liaison with the American volunteer Flying Tigers.' Perhaps because her child- hood was spent moving from one country to another - and later 'moving around the States a lot' - Wan has always been a traveller. After graduating with a BA from Stanford University, she lived in Britain, before settling in Guelph, where she obtained a masters in geography (with a focus on China's economic geography). Her career then took her all over the world, from Southeast Asia to Brazil and Zimbabwe. Although Wan's only trip back to China since leaving as a baby was in 1976, the country fascinates her. 'I find myself sometimes struggling to understand the China we're looking at today,' she says. 'Not that it's foreign to me, but it's so big and developing so quickly. I'm looking at it and my mouth is ajar.'

Wan says she may one day write her mother's story, but for now the characters she created in Deadly Slipper - the first of a planned series of murder mysteries set in the Dordogne - have taken on lives of their own. A second book, The Orchid Shroud, is due out next year. 'The plan is to have a series with the orchid theme that goes well beyond two books,' she says.

Will her characters ever leave the French countryside? 'Well, China and Southeast Asia have a huge number of orchids. Orchids are extremely widespread. They're a bit like the Chinese, don't you think?'