People today think of the 16th century as if it were part of the Dark Ages, although in historical time it's only yesterday. Many of the period's scandals were just as fascinatingly garish (and unashamedly tacky) as anything touted in last week's National Enquirer. Even more so, since those who most publicly dallied in those days with others' wives or husbands were kings and queens, lords and ladies--a far cry from the trashy hotel heiresses making the covers of magazines today.

Nowhere did sex set the fashion with more flair than in that microcosm of all that was best and worst in Europe, the French royal court. In her new book, The Serpent and the Moon, a multiple biography of a Renaissance French king and the two women who loved him, Princess Michael of Kent shows that along with the sex that made the world go round came no small share of power, if only temporary, for those women, who were both worshipped and abused as pawns on the treacherous chessboard of politics. The king was the introverted but passionate Henri II; the women were Henri's unloved wife, Catherine de Medici, of Bartholomew's Day Massacre infamy, and the woman who played December to Henri's May, his beautiful, brilliant mistress, Diane de Poitiers.

What makes the story of these people so intriguing is not just that Diane was old enough to be Henri's mother in an age when the man was usually 20 years older than his mistress, or that Henri's wife, reviled in France as the scion of Italian shopkeepers, had made the mistake of falling in love with a husband who could not return the favor. It's the fact that Princess Michael of Kent, née Baroness Marie-Christine von Reibnitz, is descended from all three personages, thus informing her insiderish scrutiny of their deeds and misdeeds.

Princess Michael (wife of Prince Michael of Kent, first cousin of Queen Elizabeth II) has written two other books about women's lot in a man's world (Crowned in a Far Country and Cupid and the King). Her Royal Highness spoke with WW recently before her visit to Portland: "There are many women--and men for that matter--that deserve to be extricated from their obscurity. I have dealt with women because I believe very few female biographers do justice to male subjects. Nor do I feel that many men write well about women." As a foreigner married into the British royal family who, because of her position, has had to answer for speaking her mind, the author is well familiar with the challenges of being an outsider who doesn't always play by the rules.

Before the princess even knew about Diane de Poitiers, she was decorating her London flat in the same black and white that Diane had so favored, even driving a black and white Mini and wearing black and white clothes. That was when the princess's mother told her about her descent from Diane de Poitiers, "who famously styled her whole life--and her whole country" in that color scheme, the princess writes.

Born in 1499, Diane de Poitiers was married off to a man 40 years her senior, Louis de Brézé. When Brézé died, she became the obsession of the king's son, Henri, for whom she had served as a sort of mother figure throughout his teen years. When they became lovers, she was pushing 40, he was not yet 21.

"It is hard to give a moral viewpoint to someone who lived in a different age," says the author. "I always try to paint a picture of the era of my subjects, not only how they lived but also of the attitudes, virtues admired and vices condemned of the day." What makes Diane and Henri's affair all the more unique is that they "decided to clean up the court on his accession. They viewed their relationship as pure."

It's a curious bit of Renaissance tergiversation. But Diane is not to be seen as a precursor to later French royal mistresses, the princess insists. Diane was still something quite apart--a woman who, in an age when women were itemized among goods and chattels, forthrightly determined her own destiny. Not even Henri's queen was able to do that.

Yet despite the author's best efforts, Diane emerges from the narrative very much a hard sell--cold as the marble statues of Diana that decorated her chateaux. As a whore to some and a saint to others, Diane is impossible to categorize. So why should we care about her now? Diane is fascinating primarily as a woman who was ahead of her time. But what most matters about this woman who died almost five centuries ago is that she was the first in a long, sometimes ruinous but often glorious tradition of elegant, intelligent women who were loved by and gave advice to the men who ruled France and who, through brains and chic, set the course of French (and sometimes world) history.

By Her Royal Highness Princess Michael of Kent(Touchstone, 432 pages, $29.95)

HRH Princess Michael of Kent lectures on her book at Whitsell Auditorium in the Portland Art Museum, 1219 SW Park Ave., 226-2811. 6 pm Tuesday, Oct. 12.

A signing and wine reception will follow in the Wells Fargo Impromptu Ballroom. Copies of the princess's books will be available at the signing and in the museum shop. The lecture, however, is sold out.