IT'S easy to see why a novelist might salivate at the chance to tell the story of Theodora, the lion tamer's daughter who became the consort of the Emperor Justinian. Here was a humbly born actress who became one of the most influential women in the history of the Byzantine empire; a former prostitute canonised as a saint.
When Stella Duffy discovered her, in a sixth century mosaic in Ravenna, Italy, she could hardly believe the story was hers to tell. "You know when you get a good idea, then three other people get the same idea and they all come out before yours? I've spent the past three years certain that something else was going to come out first."
As her book is published – uncontested by rival Theodoras – she admits that the character was every bit as much fun as she expected. History had left a few tantalising facts on which to weave a story, and a stinging account of the empress by Justinian's official historian, Procopius. "And anytime an old bloke calls a woman an evil witch and a whore there's got to be a juicy story there," she grins.
Theodora is Duffy's 12th book and her first historical novel. She has written everything from sassy female-led crime fiction to post-modern fables and gritty south London realism (her last novel, The Room Of Lost Things, was longlisted for the Orange Prize). An excursion into Byzantine history was not a direction anyone could have predicted.
"I can only write the next thing that's in my head," shrugs Duffy, 46, frank, forthright and frequently funny. "I do the next thing that excites me. This story really moved me and so I wanted to tell it."
Her Theodora grows up within the rigorous training regime of the Byzantine hippodrome, as much circus and spectacle as conventional theatre. By the time she is in her teens, she is an acclaimed comic performer. Duffy, who worked in theatre and improvisation before she turned to fiction writing, relished the chance to write about the stage.
But the hippodrome had a darker side. From puberty onwards, the young women were expected to earn additional money working as prostitutes. It was this early experience of abuse which, Duffy believes, inspired Theodora to work with Justinian to reform rape laws and improve women's rights (part of the sequel, on which she is working).
"I found all that very difficult to write," she says. "Of course I think it's profoundly wrong, but it's also how that society was run. I decided I had to write about it, because otherwise I'd be lying about Theodora's truth, the details which formed her."
In her mid teens, at the height of her popularity on stage, Theodora quit Constantinople with her lover, Hecebolus, who was made a governor in Africa. But the relationship did not last, and Theodora found herself on the road, living off her wits, until she took refuge in a Christian community in the desert near Alexandria where, the history books say, she underwent a religious conversion.
This, Duffy admits, is another challenge to a modern audience, but "to be true to Theodora" she needed to include it. "I was brought up Catholic and I've been practising Buddhism for 24 years, so the questions of faith really interested me. I'm interested in how people with really strong spiritual beliefs manage to live a day-to-day life with that, and clearly Theodora did. In many way she's so modern, shagging and falling in love and having affairs, speaking up for herself and being what we would call a feminist. But then to have a religious life, a spiritual life, gives me loads more layers to play with as a writer."
Duffy says she owes her prolific output partly to the discipline of her Buddhist practice and partly to the work ethic of her parents, timber mill workers in Tokoroa, New Zealand. "My dad was a labourer, he worked from when he was 14 and the only time he had off was when he was a prisoner of war in Germany for four years. I don't kid myself that I'm doing what my parents did, but I'm very grateful for what I have, so I do try to make the most of that and get on with it."
The youngest of seven children, she was the first in her family to go to university, and – much to her parents' disappointment – headed straight into a job with a travelling theatre company. "My dad didn't cry when I came out (Duffy married her partner, the writer Shelley Silas, as soon as civil partnership became legal], but he cried when I said I wasn't going to be a lawyer or a teacher. For him, that was a waste of the gift of education. For me, the gift of education was so special because I was then free to do what I wanted."
Aged 23, she went to London and joined impro company Spontaneous Combustion, which included Patrick Marber and Jake Arnott. "Impro taught me to write," she says. "It gives you a whole bunch of techniques for freeing yourself up, for trusting yourself. If you make a mistake it's all right, and maybe you'll learn something from it. The magic is always in the mistakes." She says she treats the first draft of a novel as an improvisation exercise, honing and reworking up to four further drafts.
And she continues to work in theatre, appearing in Improbable's Lifegame at the Lyric Hammersmith in July, and developing a "big project" with the National Theatre Studio. "Twenty years ago, I was mostly an actor who sometimes wrote, now I'm a writer who sometimes makes theatre. It's great that I do something which allows me to change. In 20 years' time, or 40 years' time – who knows?"
Theodora is published by Virago, 14.99