"He'd read the book overnight and he really wanted to meet me. And that was how it started. I had a publisher and the next thing I knew, I was on a plane to Hollywood," she tells The Sunday Times over the telephone from Italy, a stop on her packed book tour around Europe. "I'm still in disbelief."
The American rights to Maestra - the first book in a planned trilogy - went for a seven-figure sum. The film rights were snapped up by former Sony Pictures chair Amy Pascal even before the book was published. The book, a potent mix of murder, intrigue and sex, follows Judith Raleigh, an assistant at an art auction house who is sacked after she discovers a forged painting. She soon finds herself swept up in a killing spree around Europe.
Maestra has launched a second career for Hilton, an Oxford graduate who has, under her real name Lisa Hilton, churned out nine history-heavy tomes, including a book on the lives of England's mediaeval queens.
"I think my agent was rather worried that this kind of book would mean that no one would take me seriously as a historical writer," she says. "But I really didn't think that was a problem, firstly, because I don't think anyone really cared about my history books. And I also don't see why it should be impossible for someone to write something completely different from what he is known for."
And she has not strayed far, she insists. Maestra, too, is packed with history, but that is "well disguised", says Hilton with a chuckle.
The book has drawn comparisons with thrillers such as Gillian Flynn's Gone Girl and now rests comfortably at the top of bestseller lists worldwide.
But Maestra started off as an odd mish-mash of rejected manuscripts, says Hilton, a divorcee with a 10-year-old daughter.
About two years ago, her agent asked her to take a stab at writing something erotic. But when it was done, "my editor absolutely hated the entire thing", recalls Hilton.
The manuscript was stashed away, forgotten, as she carried on with her biography on Queen Elizabeth I. "Then I finished that and I wanted something else to work on. So I took out the pages of that erotic novel and I had another manuscript I'd begun many years ago. There they were: these two reject manuscripts, one an erotic tale, another about a fake painting," she says.
"What would happen if I put them together? That was how the story started."
She breezed through the writing, finishing the book in about two months. Her research included flying to Geneva to interview a banker about how to move money around, and attending a sex party in Paris.
"I think that if you're going to write about something - anything - it's important that you get the details right," says Hilton. "And I'm glad I did go for this sex party because my idea of what it would be was different from the reality. I imagined it would be something rather sordid, but it was actually elegant, discreet and quiet."
Although Maestra is a cleverly crafted thriller that weaves in threads of more sombre topics, such as art history and the politics of gender and class, some readers have been quick to harp on the sex scenes.
People tend to react differently when a man writes about sex, compared with when a woman does it, says Hilton.
"I think that men are allowed much more freedom and licence in what they do to bodies both male and female. If we look back into the 1970s and 1980s at writers such as John Updike and Philip Roth, they were writing explicit sex scenes and they were treated as great literature, as serious art," she says. "Whereas I wrote a sex scene which is graphic and that scene is shocking and disgusting. I find that strange.
"I also find it strange that in crime fiction - if you look at work from Scandinavian crime writers such as Jo Nesbo - they describe horrible disgusting torture being inflicted on women's bodies," she says.
"You can write about killing a woman in all sorts of horrible ways, but somehow if you write about a woman who enjoys her own body and no one gets hurt, that's shocking."
And to reviews that have been quick to compare Maestra with E.L. James' Fifty Shades Of Grey, Hilton, cool, calm and eloquent as ever, says: "I think that's just wrong."
James' book is at its heart a love story: a young, powerless woman falling for a dominant older man.
"Their relationship is the focus of the book. But my book is not a love story. I think there should be a big notice on the cover: 'This is not a love story'," she says with a laugh.
She adds: "This again is an example of the way in which women writers get put in boxes all the time. There seems to be a need to categorise women writers which just doesn't apply to men.
"It's kind of an unfair comparison to both books. I feel sorry for readers who've bought this book hoping it will be Fifty Shades Of Grey because they must be very disappointed."
- Maestra is available at $26.75 from major bookstores.
