In her captivating new historical novel, The Birth of Venus (out last month from Random), set in Florence during the Renaissance, Sarah Dunant's heroine acts bravely and decisively to save the man she loves, putting both of them in grave danger. It's the ultimate risk in that time and place, with fire-brand preacher Savonarola's night police patrolling the streets, arresting and torturing anyone suspected of committing a sin.

British writer Dunant's own risky decision—to break out into a new genre—also involved a love affair. In her case, it was the end of a passionate relationship that she had expected would last the rest of her life. The author of several previous psychological novels and three mysteries was in Florence during the millennium week when the affair ended.

One of the most dramatic moments of what was clearly the beginning of the end took place in a restaurant just off the Piazza Santa Croce. "I sat at the table with the remains of my bloody steak and my bloody relationship," Dunant recalls. "Here I was at the beginning of a new century and a new decade in my life. And I thought: what am I going to do with my future?"

Few people would have acted as decisively. Dunant realized that whatever her situation, she never felt bad when she was in Florence: "It's something about this city with its intense beauty and its style and flamboyance." Immediately, she decided to buy an apartment there to live in part of the year, and, indeed, quite soon she found a tiny apartment just off Santa Croce square. By the time summer rolled around, she was able to spend time there alone. She immersed herself in books about the history of Florence, while walking everywhere that the pivotal events of the 15th century took place.

By the end of that highly charged vacation, Dunant says she had begun to understand the early Renaissance—how it changed the Western world. "I was already thinking it would be wonderful if one could find a way to re-create that moment, so it would be like living through this extraordinary period." As her novel would later illuminate in vivid detail, this was an era when many Florentines were exceedingly wealthy, worldly, and well educated. Lorenzo de' Medici and others commissioned magnificent art from the painters and sculptors. The rise of the aggressively pious monk Savonarola, who fulminated against the corruption of the established church and the excesses of upper-class society, shook Florence like an earthquake. Adjured by the fiery priest to divest themselves of fine clothes, jewels, books and works of art (these worldly possessions were incinerated in the Bonfire of the Vanities), the rich citizens of Florence endured a period of profound fear and confusion.

Dunant was mulling over the turmoil of that time when her two daughters arrived after having spent some weeks with their father. "The 13-year-old was attitude on a stick," she says—ready to shop but not to "do culture." The 10-year-old had not yet acquired teenage cynicism and was able to be amazed. Their different attitudes—one feisty and independent, the other in awe of the magnificent art she was seeing—crystallized Dunant's focus. She found herself thinking about the young women of the early Renaissance, some of whom surely had "ability and talent and confidence and a feeling that the world was opening up to them," and yet were relegated to early marriage and motherhood. These women were well-educated and obviously appreciated art, as evidenced by the paintings that many of them commissioned.

The paradox of a protected life that stifles ambition crystallized in Dunant's heroine, 14-year-old Alessandra Cecchi. Realizing that she has the talent to be a good artist but denied the opportunity to develop her skills, Alessandra uses subterfuge and a fateful relationship with a young painter who's been engaged to create frescoes in her family's chapel to find her own artistic path and to wrest her freedom from a hastily arranged marriage to an older man. Meanwhile, the situation in Florence is dire. Fra Savonarola is preaching fire and brimstone, castigating the Medicis for their sybaritic lifestyle and intellectual vanity and calling on artists to rid their works of pagan elements.

The artistic achievements of such artists as Ghirlandajo, Donatello, Masaccio and Botticelli provide some of the rich, sensual background that Dunant effortlessly integrates into her narrative. Her research—some 19 volumes in the bibliography—took only six months, since she came to the project with basic knowledge. Having read history at Cambridge, she had the skills to analyze the period, although she says she was concerned about her ability to describe the era's turbulent events in a fictional form. She also had academic training in art, having studied painting until the age of 18 with a gifted teacher whom she thanks in the novel's acknowledgments.

Part of her research included reading Savonarola's sermons—what she calls the "official stuff." Then she came across a couple of court cases about the treatment of homosexuals and prostitutes—the "subversive internal history." Further sleuthing uncovered a book about the policing of Florence during the 15th century. "The most interesting thing about this period is that everyone believes in God, but everyone sins," she says.

The book's title, of course, comes from the famous painting by Botticelli that now hangs in the Uffizi. While the painting itself figures only marginally in the novel, its significance is as a symbol of the new kind of art the Renaissance engendered. "It is the Renaissance," Dunant says. Although now it's become almost degraded by being reproduced on mouse pads and tea towels, the painting has historical significance because it's one of the first pictures in which the subject does not have religious significance, depicting instead the pagan Venus of classical mythology. Before that painting, Eve had been depicted as naked, but her nudity represented her shame.

To Dunant, the painting is the beginning of a journey about women's sexuality. TheBirth of Venus is about desire and how women deal with that desire, sexual and creative, she says. "Although Botticelli's Venus is now almost iconic, very few people would have seen it at that time, since it was privately commissioned and kept in the owner's villa," Dunant says. Good thing, too, Dunant observes, since Botticelli was convinced by Savonarola's sermons that he had transgressed against God and may have burned other paintings with mythological subjects. His later paintings all adhere to religious subjects and lack the creativity of Venus, Dunant observes.

More central to the plot of her novel are Botticelli's illustrations for Dante's Divine Comedy, which Dunant was unaware of when she started writing. The illustrations, which had been commissioned by one of the Medicis and later scattered and lost, were the subject of a recent exhibition at London's Royal Academy of Art—the first time all the extant paintings had been brought together. Walking through the exhibit, Dunant was particularly struck by the depictions of hell. "There were 200 souls running across the burning ground, all in terrible pain." The pictures helped her to imagine the reaction of Florentines to Savonarola's doomsday predictions.

It was inevitable that once she began her research, Dunant would see parallels between 15th-century Florence and the wave of fundamentalism sweeping the Middle East. She didn't draw overt comparisons, however. "I think there's a danger when you set out to reflect contemporary politics in historical fiction. Good fiction needs freedom of the imagination rather than the prescription of ideology," she says. Yet when she discovered that Savonarola forbade women to come to church, lest they distract the male worshippers, and relegated them "to be kept in obedience, chastity, and silence," she couldn't help thinking of the Taliban in Afghanistan.

Dunant may not write with an obvious message, but readers have learned that her books always deal with issues confronting society. Her Hannah Wolfe mysteries have explored such topics as using animals for research and the dangers of cosmetic surgery. Her concern with such themes is an outgrowth of her 20-year career as presenter, or host, of radio and TV programs dealing with high-brow cultural topics. "I have always believed that there is nothing so complicated in the world that can't be explained," she says. "But from the very moment that I began to write thrillers and mysteries, I knew that I wanted to write fiction that dealt with issues in a popular form." She deplores the profound abyss that seems to lie between pop novels and literary works, especially in England and believes her own work bridges the gap. "I choose to discuss serious issues through a damned good story." That people sometimes say that her work is too intelligent to be popular, or too popular to be literary, proves the point.

Reading Dunant's three Hannah Wolfe mysteries (Birth Marks, Fatlands and Under My Skin) before coming to TheBirth of Venus reveals the range of her literary skill. Infused with dry wit and psychological insights, the mysteries are taut, lean and swiftly paced, while Venus is often lavishly descriptive, rich with sensuous detail and almost painterly in depicting scenes and atmosphere. Dunant says that writing the Hannah Wolfe books was one of the best apprenticeships a writer could have: "It made me realize how important the structure of the story is. Your style must be eloquent and muscular, and you must force your reader to read fast. Writing Venus allowed me to touch the fabric, as it were. It allowed me to slow down so the reader can luxuriate." Even so, the plot of her historical novel contains three mysteries, all subtly suggested and revealed with a sinuous grace.

Right now, the 53-year-old Dunant is multitasking. She's currently adapting two of her recent books—the psychological thrillers titled Transgressions and Mapping the Edge —for two British producers who have optioned them for the movies. She has given up her journalistic work for the BBC because she thinks her teenage daughters need more of her time and active parenting. Indeed, her phone conversation with PW is interrupted with some domestic questions from one of the girls about what food goes in the freezer—part of a New Year's resolution, she tells us, to have them assume some household chores. She's also gearing up for her 10-city U.S. book tour. Dunant credits her editor, Susanna Porter, whom she followed from Bantam to Random House, for understanding and championing her work. She calls her relationship with Porter and with the Random House publicity department "the gold dust in the publishing business. Without that kind of support, your book is just 400 pages between hard covers."

"The signs for The Birth of Venus are good," said Porter some time before the book came out. Since then, the novel generated plenty of industry buzz and has now leapt onto bestseller lists. Porter credits Gina Centrello with recognizing the in-house enthusiasm for the book and deciding to create the kind of promo campaign usually employed for commercial fiction rather than for a literary novel. "That's one of the pluses of the Ballantine connection," Porter says.

Mulling over her next project, Dunant is pretty sure that it won't be a mystery. When she created Hannah Wolfe, female private eyes were very important as a kind of creative wish fulfillment. Now Dunant says she's more interested in the complexities of women's existences. "There's an awful lot to learn about who we are now. I'm interested in asking more questions."

And to take the kind of risks that have motivated her fiction. In fact, she tells PW, the prologue to The Birth of Venus was an act of near -desperation. Having completed her research, she had "become very scared that I couldn't write the book. My children were away for the weekend, so I sat down to write something. Suddenly there was this nun with this serpent painted on her body. I did not know how it got there. I wrote the book to solve the puzzle I had set. So you could say that the city and story found me rather than the other way around."