As part of the novel's pre-publicity, her publisher's PR e-mailed a blog piece Barker had recently written entitled "Six dramatic, nomadic years with a half-finished manuscript in my head". It began: "During the six years I spent writing my novel , I lived in seven cities in four countries. I moved in and out of 17 different houses and flats in Beijing, Seoul, Colorado, Boston, Leeds, Washington DC, London and Shenzhen." The last line was: "So, this year, as thoughts turn to ideas for a new book, I also intend to expend some mental energy on making plans for the future too: to choosing a place to settle down, and to putting the years of drifting nostalgically in the past."

When this interview was first suggested, at the end of May, Barker was living in Shenzhen. I'd hoped to meet her there but she was packing up her things and, by early June, she was in Beijing again. (In 2009, she moved five times within the capital.) She then flew down to Hong Kong for a couple of days, in mid-June, to renew her visa and we finally arrange to meet. A couple of times, during our subsequent conversation, she mentions that she'll find out, in a few hours, whether she'll be able to return to Beijing. The travel agents have warned her that visa rejections are currently on the high-ish side and it seems likely that she'll have to change her plans - but she's impressively sanguine.

"I've done it so many times," she says, philosophically. "It's always like this."

We meet in Starbucks, next to the Hotel Ibis in Sheung Wan, where she's staying. It seems possible that she'll arrive trailing mountains of luggage but she's unencumbered - a slender woman of 36, in a sleeveless dress, with a small handbag, a tattoo on her left arm and, initially, an air of reserve. She hasn't done many interviews and here's the proof: she offers to buy her own coffee. She also doesn't trot out pre-prepared spiel. I am quite struck by the gap between blogger and Barker. You get the impression that the references in that blog-piece - to pet-sitting a fluffy white cat called Mr Cookiepants in Washington, for example - plus its cinema-trailer title ("Six dramatic, nomadic years …") are part of her polished, re-drafted writing world, not her real world. Or at least a real world that involves being interviewed.

Has she ever written in a coffee shop?

"I wrote in coffee shops in Japan when I was 22, 23, before I had the stamina to sit down and write," she says, glancing round. "I liked the buzzy environment; I couldn't speak Japanese when I arrived so it was kind of a white noise. It felt more sociable than being alone but, now, as I've developed a writing practice, I couldn't do it."

She was in Japan to teach English and it's where the notion of writing fiction seems to have come upon her by accident. Yes, she read as a child, but she's scrupulous enough to point out that it wasn't voraciously.

"You know, you hear about these writers reading at 12. I wanted to be a chemistry teacher."

Growing up in London, she and her younger sister, Carol, lived with their mother, a nurse who'd arrived in England from Malaysia in 1969. The girls' father is English but her parents separated when Barker was five.

"They used to fight a lot. I don't remember it as being traumatic and we saw him every weekend. It seemed quite normal." (Amid the psychological mayhem of , there's an eight-year-old girl whose parents separate and who, by the end, has become a poignant presence. The child's name is Echo. "Perhaps I'm channelling childhood stuff but I'm not conscious of it," Barker says.)

The family lived in east London, which has not always been known for its racial tolerance. Although Barker talks about the area ("It's become multicultural but it was quite white then"), she e-mails afterwards asking that it not be mentioned. In fact, she says, she didn't encounter overt racism.

"I never really felt I fitted in but the whole point of being a teenager is that no one gets you. And a lot of people didn't realise I was half-Chinese."

Did she?

"I knew we were different. We'd have rice for dinner and then you'd go to the houses of English friends and have Sunday roast. I had a lot of Asian friends, from India and Pakistan, and their households were a bit culturally cocoonish. You learn to be a cultural chameleon."

The girls travelled "a lot" to Malaysia during their childhoods. "Malaysia was a big part of our mother's identity. But we both felt quite culturally dislocated from China."

In her mid-teens, she worked weekends at McDonald's, where a fellow employee, who was Chinese, introduced her to manga, which fanned an interest in Japan. At 18, she went to Nottingham University to study chemistry, dropped out, worked for a while as a waitress, then went to Leeds University, to study politics and philosophy.

"[It was] a steep learning curve after science," she says. "I remember the tutor handing me back the first essay I wrote and saying, 'This isn't an essay, it's a list.'"

Having become involved in student journalism, she decided that line of employment could be for her. The JET (Japan Exchange and Teaching) programme was a way of seeing Asian life - as a teaching assistant in a town 20 minutes outside Kyoto - while applying for journalism courses in Britain.

"It was my first real experience of feeling very white, very conspicuous. I kept a journal for a year because I wanted to describe it to myself, then I started writing fiction. I didn't want to write an autobiography and I wasn't interested in writing about expats."

She finished her first book while doing an MA in creative writing at Manchester University, paid for with money she'd saved from Japan. Manchester had replied to her while she was still waiting to hear about a journalism course. "It was a twist of fate - I could have been a journalist."

When told how supremely lucky an escape that was on the earnings front, she replies, with equal feeling, "Fiction writers have to struggle as well." Some, however, have to battle on longer than others; in Barker's case, a literary agent came to Manchester to give a talk and, in the pub afterwards, she told him what she was doing. He asked her to send him some chapters. Then he found her a publisher, Doubleday, part of the Random House group.

The original title of the book was , which was a very good idea until the morning of December 26, 2004, when it became a very bad idea.

"Doubleday were brilliant, they reacted quickly." Publication was delayed for a month and, as , the reviews were encouraging ("Highly original … A major achievement by an exciting new author": ) and it was longlisted for the Dylan Thomas Prize, as was her second book.

"When people say they must read the other books, I say, 'You don't have to,'" she remarks, quietly. "I feel is very distant, I don't remember the characters."

Despite her advice, I later read which is now available in bookshops here ( is available only online), and am retrospectively surprised by that comment because her second book seems much closer than her first to actual events in her life. One of the principal characters is a young Malaysian woman called Frances, who comes to late 1960s London as a nurse, marries an Englishman and has two children; one of the backdrops is an east London housing estate, vividly - and bleakly - described.

After I'd finished it, I e-mailed Barker and asked her about the overlaps. She replied that some of her mother's life had inspired the creation of Frances but that "Frances is quite a passive character whereas my mother is quite strong and fiery". She added that she'd been nervous about showing it to her mother "but she didn't say anything, just that she'd liked the book. (My sister later told me my mother had told her she had found the book 'boring' and skim read it)". Again, that aside - with its sly humour and timing and hints of family dynamics - seemed exactly the sort of comment Barker was comfortable writing but wouldn't have uttered.

- or the title-less, barely-formed notion that would eventually mutate into - brought Barker to Beijing in 2007. She wanted to live in China (to the bafflement of her mother, whose father had left Guangdong province for Malaysia in the 1940s); she hoped to write about both imperial and contemporary China; and life in Beijing was much cheaper than in London. She'd learned to speak some Putonghua in England but, unfortunately, hadn't bothered with tones, so was effectively incomprehensible, and she couldn't read any characters. The plan was to stay for about a year, maybe two.

In 2008, a shift in mainland visa regulations, pre-Olympics, kyboshed that. She went to South Korea, where her then-boyfriend had a teaching job with free accommodation. There were overseas offers to house (and fluffy cat) sit; she was sufficiently broke that even with the cost of international flights and storage, the upheaval was worthwhile.

"I moved a lot for financial reasons," she says. How on earth did she keep working? "It took six years and the moving probably slowed it down. It always took a while to re-immerse myself." For two years, between 2010 and 2012, she was back in Leeds, in the north of England, on a Royal Literary Fund fellowship, which helped; the book was finally finished at the beginning of this year, in Shenzhen, where her American boyfriend was working for Huawei Technologies.

Inevitably, passed through many drafts. The manuscript, which she always printed out in its latest revised version, she says, and carried with her everywhere, was the one constant handed down as she lived her various global lives. ("When I couldn't work on it, I was lost," she wrote in her blog.)

"This book is the one I put all my energy into," she says.

And it's an absolutely gripping read. It's a tribute to the zing of the writing that every time a section ended, usually with violent abruptness, I craved more (especially, appropriately enough, in the opium war part, which seemed to finish before it had quite begun). Did the episodic nature grow out of its creator's peripatetic lifestyle?

"No, I like to jump about between different people's perspectives," she says. "The truth is a multiplicity of viewpoints. And Chinese history is so rich with narratives of war and revolution I wanted to write about several of them. In order to do that I had to introduce a short-story structure."

There's also a number of brutal couplings. The seriously toe-curling section on the Jiajing Emperor and his concubines - and his scalpels - prompted an immediate Wikipedia check by this reader to see if that tale was true. (It is.)

"People are always asking me about the sex," Barker says, smiling. "I'm very surprised about that, I still don't really see it as explicit. Sex is a huge part of human nature. I'm surprised that people don't write more about it. This guy from Reuters, a friend of mine, said, 'How about this major theme of homosexuality?' and I said, 'Wow, I didn't see that as one of the major themes.'"

She pauses, thinking about her own act of creation. "I feel uninhibited when I'm writing."

Does she believe in reincarnation?

"I don't think so but I'm open to the possibility. Life is frustratingly short and I realise that as I get older. At the same time, reincarnation into medieval times when life was Hobbesian [i.e. nasty, brutish and short] isn't so appealing. Reincarnation was a device to bring historical research into contemporary China, that's why I introduced it. But with each redrafting of the book, the reincarnation aspects became more substantial. It linked in with the theme that history is cyclical. We repeat ourselves."

And what about the ghost fixation, a theme that runs through all three books? She laughs.

"No, I haven't seen one but I can spook myself easily, I'm very susceptible. I'm drawn to the supernatural. That's from my family in Malaysia, where there's a climate of belief. One of my aunts hired Buddhist priests to chant to get rid of a woman ghost who'd lost her baby and would cry at night.

"When you're 11 and you hear one of your aunts at breakfast talking about how she saw a man with red eyes staring in at her, there's no cynicism."

The photographer arrives to take portrait shots. Barker, who has offered to provide an existing set of photos and is obviously ill at ease with the process, agrees to one suggestion; and says no, quietly but firmly, to another.

"I was a pain in the arse in my first year at Leeds," she'd confessed earlier. "I'd started learning about political ideology and I was boring on about being working class." There's no sign of that bolshiness during this interview; but there is, perhaps, an understandable desire to have some control over her life.

"I feel creatively very spent after this book," she says, standing in the hot street. "I haven't written any fiction since I finished in January this year. I don't have the energy or the courage."

History being, indeed, cyclical, her boyfriend is moving back to the United States - to Indiana - for his studies so, despite what she wrote on her blog, she's going to be on the road again soon. "I'm unsettled now. It's so ironic - I like domesticity, I'd like to settle down."

In the sunlight, the tattoo on her left arm is more visible.

"I got it done at 18 or 19, when I used to be really into rock music and night clubs," she'd said in Starbucks. "It's a Celtic symbol. I still like it. Ask me in a decade if I still like it …"

At the Man Mo temple, on Hollywood Road, encouraged by her interviewer, she makes a donation, beats the drum, rings the bell. Her summer plans - talks in Shanghai and Beijing as well as an appearance at the Hong Kong Book Fair, in partnership with the British Council, on July 20 - are an edifice built around a successful visa application. Which - she learns later that afternoon - has been rejected. As a result, she misses her flight to Beijing.

The following day, she tweets: "Is there a shrine in Hong Kong where I can pray to/bribe the gods of China visa bureaucracy?"

But she's been on this path before. She makes a second application, for a different visa. A few days later, she e-mails from Beijing to say she's made it back again. She is, she says, very happy.