But when it came to real life, the Edinburgh-born writer was fairly sure that her own family story was rooted quite clearly: Russian Jew on her mum's side, Irish Catholic on her dad's.
Now, though, a simple DNA test has blown apart fact from fiction. And the unexpected results of her own life story have left her with an even bigger mystery to solve - of exactly who she is and, more perplexing, how on earth she ended up here.
"I didn't anticipate the outcome at all," admits the author, whose DNA findings have just revealed she is actually an Oriental genetic rarity most probably descended from a captured slave from a tribe so unusual that finding them had left scientists scratching their heads for months.
The irony of being at the centre of a historical conundrum created by her own DNA is not lost on the writer. "My job as a historical novelist is usually to embellish facts like crazy to make a story," she smiles, "and now I'm finding myself having to strip everything back to try to get to the facts."
Her mother's family's Jewish faith led her to assume their origins were somewhere in the Middle East. Results from ScotlandsDNA, a research project which is compiling a genetic map of the nation, instead revealed she is one of a "vanishingly rare" female line that developed 17,000 years ago in the area around Sakhalin, Japan's most northerly island, and were eventually taken as slaves.
Incredibly, this new found real-life background has faint echoes of a story from one of her own novels, Secrets of the Sands, which tells how a young Abyssinian woman is forced into slavery.
The findings were revealed after 11 painstaking months of research which, according to Alistair Moffat, managing director of ScotlandsDNA, had scientists scratching their heads. "It's incredibly rare to see this," he says. "There is an amazing amount of diversity in Scotland's population and Sara's findings have just made it even more diverse. It really is surprising."
Eventually trade with other countries led to the introduction of disease, claiming many of the tribe. Ainu women were captured and taken into slavery as the island fell into Russian control, while centuries of intermarriage and movement means the precise number of true Ainu is unknown. In the mid-19th century, there were only around 17,000 Ainu people left.
Sara was unaware of the ancient tribe when she took the DNA test last year. "My husband organised it as a birthday present last June, he'd heard about work to map Scotland's genetic heritage and how people were finding out how much of their background was Viking or Pictish. All that was right up my street," she explains.
She provided a saliva sample and expected to hear within a few weeks. "After three months when I chased my sample I was told that I was 'unusual' and that geneticists and historians were working on my case. My husband was joking with me, saying they'd discovered I was really a sea creature or a hobbit. I even thought that as it was taking so long I should ask for my money back."
In fact, scientists had hit a wall as they scoured the globe in a bid to match information contained in her mitochondrial DNA - the strand passed from mothers to their children.
"We get six billion letters of DNA - three billion from our mother, and three billion from our father," explains Alistair, whose organisation has now mapped more than 7000 different DNA samples. "Sara's DNA had what we called a Sakhalin marker, after the island where it's most commonly found."
Sara's search for more detail led her to online images of Ainu women and she was immediately struck by the physical similarities she shares. "One particular tribe was famed for physical features that endure in my family today - very thick hair and wide cheekbones. Somewhere along the slave route that runs along the southern border of Russia one of my female ancestors - likely a slave - whose mother and grandmother and great-grandmother might well have been raped and abused by men on the route - of many genetic persuasions - must have met a Jewish bloke.
"This history may not be that distant," she adds. "Russia abolished slavery in 1723 but serfdom continued until the 1860s, the decade incidentally when my own great-grandmother was born."
The DNA discovery has made the author keen to unravel her father's side of the family - a test that will have to be undertaken by a male member of her family. "I always thought that bagels and lox was my soul food but it turns out it's sushi. I had envisaged ancestors who had survived slavery in Egypt, not on the Steppes. It's made me realise how insubstantial are many of the stories we create about ourselves. It turns out that I not only write fiction but I am fiction too. My identity is more complex than I'd imagined."
Discover your DNA story. Visit www.scotlandsdna.com
'Immigrant' genetic make-up in every Scot
WE all carry six billion DNA letters, three billion from our mother, three billion from our father.
Fathers pass on Y chromosome DNA to their sons and mothers pass on mitochondrial DNA, or mtDNA, to their sons and daughters. But mtDNA dies with men and it survives only in the female line.
It means researchers can read two ancestral stories in men's DNA, one for their Y chromosome lineage and one for their mtDNA lineage. In women they can only read only their mtDNA story.
Tiny blips known as markers can appear which reveal fascinating detail about precisely where a person's ancestors came from and pinpoint when they lived there.
Unravelling the information means scouring DNA databases around the globe.
Britain has a rich and diverse genetic make-up drawn from across Europe, Asia and even Africa. Unpopulated until 11,000 years ago, it means every Scot has some kind of "immigrant" make-up.
Tom Conti has link to Napoleon Boneparte
AUTHOR Sara Sheridan has discovered her roots lie far away in the east, however DNA research among Scottish men has revealed ten per cent are directly descended from the Picts.
Researchers at Melrose-based ScotlandsDNA found a Y chromosome marker suggesting a large number of descendants of northern tribes known by the Romans as "picti" meaning "painted ones".
The fatherline marker, labelled R1b-s530, was found to be ten times more common in those tested who had Scottish grandfathers than those with English grandfathers.
The project has tested more than 7000 people, some from as far away as New Zealand and Australia, since it began 18 months ago.
The hope is to eventually draw up a "map" of Scotland's genetic make-up.
"Every result is interesting," says managing director Alistair Moffat.
"We are already finding that Scotland is incredibly diverse with more than 100 lineages already found.
"It turns out we are all very, very different.
"Because we are on the edge of beyond, people tended to move westwards and this was as far as they could go.
"We have found a lot of men descended from Berber and Tuareg tribesmen from the Sahara.
"But that just tends to throw up even more questions than it answers about how that has happened.
"We simply don't know.
"There is also a substantial group of women in Scotland originally from central Siberia."
More than one per cent of all Scottish men are descendents of the Maeatae, a Scots tribe whose historic homelands were near modern-day Stirling.
And Alistair's own DNA marker from his Hawick-born mother's side revealed Pakistan connections and English roots on his father's side.
When ScotlandsDNA tested Scots-Italian actor Tom Conti, the findings revealed the astonishing link with a relative of Napoleon Bonaparte, while an ancient ancestor of Scots radio presenter Fred MacAulay is thought to have been sold as a slave in Dublin in the ninth century and then brought over to the Hebrides.
The DNA of the Duke of Buccleuch was found to be an exact match of a descendant of Charles Stewart, who fought at the Battle of Culloden, with both men descended from a Breton aristocrat, whose family came to Britain in 1066 with William the Conqueror.
DNA research costs from £170, and the results are added to the genetic map of Scotland.
The test process involves a small saliva sample which is posted to ScotlandsDNA headquarters and then analysed.
Appeared Edinburgh Evening News May 2013
(c) 2013 Johnston Publishing Limited
