IMAGINE a beautiful, intelligent, sweet-tempered girl born into the second most powerful family in England, guided firmly at age 17 into marriage with the heir of England's most powerful family, a fellow eight years older, remote, reserved, seemingly unaware of his bride's singular qualities, and very nearly a prisoner of the social and public demands of his title.

The girl's affectionate, romantic nature, inherited from her adoring mother, would not let her believe her union was other than a love match, though it was obvious to others that despite a ritual courtship, genuine passion was not a part of it. Bluntly, the marriage was the best deal imaginable economically, politically and socially for the two families.

And so: apparently bored with his bride's company, though she did everything save stand on her head and whistle "God Save the King" to please him, the man returned to the fellowship of his sporting chums, the masculine comfort of his clubs, and of course his mistresses, leaving the baffled and hurt but steadfastly cheerful (at least in public) young Mrs. to her own devices. (Young Mr. did, however, relentlessly bed her in the wee hours in bold pursuit of a son).

Seek and devise your own society, she was told, essentially. Seek and devise, she did, with a vengeance.

Within a couple of years our girl was fashion's darling; what she wore became a must have for every society dame and damsel. Her beauty, sincerity and amiable personality won her admirers throughout the gentry and her general populace (though in private she suffered eating disorders and occasional hysterics). She was barely out of her teens when her fame eclipsed that of her phlegmatic husband.

Is this beginning to sound familiar?

Family Resemblance

Well, if you said Princess Diana, tragically dead these last two and a half years, you're halfway there. Our girl's name was Spencer, too and she lived at Althorp, the family estate where Diana was raised and is now buried. She was Georgiana Spencer, Lady Di's great-great-great-great aunt, born in 1757 and wedded to William Cavendish, the fifth Duke of Devonshire, in 1774. Any number of parallels between Diana and her ancestor are readily apparent in Amanda Foreman's exciting "Georgiana, Duchess of Devonshire".

But this book is not a romantic confection comparing two lives (Princess Diana is mentioned only on the dust jacket). This is an elegantly written winner of Britain's Whitbread Prize for biography by a young scholar who did an immense amount of work on a ton of primary source material, plus an impressive list of secondary-source books.

The Duchess is fortunate in having her reincarnation, in the pages of a book, fall into the hands of Ms. Foreman, who, like a superb actor who cannot be seen "acting", re-creates a world without intruding herself into it. She does not give us Amanda Foreman being archly clever and condescending at the expense of her defenseless subject. She gives us the Duchess of Devonshire, in a rendering to skilful that it brings to life the winsomely lovely woman in the Reynolds portrait so superbly reproduced in one of the three large photo sections of this attractive book. Ms. Foreman's intelligent insights on domestic, social and political aspects of this time and her judicious psychological interpretation of her subject's behaviour flow smoothly, and with no pontificating, into the story.

And such a rendering is important, for there is a significance to this biography that transcends what may seem in the early pages a mere, but very entertaining, chronicle of a fabled aristocratic playgirl in an age of gilded, and often immoral, extravagance. And that is because the duchess, as she quickly matured in her late 20's, became a political force to be reckoned with at a time when women, as Ms. Foreman writes, "could not vote, were barred from the House of Commons and could not hold an official position".

Excerpts from Georgiana's passionate, moving letters add considerable drama to the story, particularly the bizarre menage a trois of the duchess, the duke and Lady Elizabeth "Bess" Foster, the woman no-one could resist.

From the late 1770s to 1806 the Duchess of Devonshire was as famous in England and in France, where she was a friend of Marie Antoinette, as Ladi Di was in the world at large. Her frenetic entry into the game of life "coincided with the flowering of the English press" which found that reporting on Georgiana and her Devonshire House Circle and its giddy whirl of balls, drinking binges, gambling and sexual nanky-poo was a marketable quantity.

Georgiana and her followers were a sort of "cafe society" within the ton, the exclusive party-going and -giving society of aristocrats who were the arbiters of taste and cultivation. They had "a passion for the theatre and a love of scandal". And scandalous notoriety they got when one of their own, Richard Sheridan, satirized them in "The School for Scandal" (Georgiana was Lady Teazle). But the Devonshire gang loved the joke and went to opening night to laugh at themselves.

What they couldn't laugh off was the economic ruin many of them brought upon themselves by their compulsive gambling, principally at faro, that sometimes ran through multiple days and nights, until exhaustion or bankruptcy felled them. Georgiana was one of the most addicted, jeopardizing her marriage, her husband's fortune and her reputation. It was a lifelong curse; she could not walk past a gaming table.

Georgiana was to a great extent saved from this slough of dissipation by two things; the requirement by the great families that their women campaign for the candidates that the families supported; and her friendship with the flamboyant Charles James Fox, the great but greatly flawed leader of the Whig party.

Vicious, Violent and Corrupt

The Spencers and Cavendishes, as it happened, were ardent Whigs and "Foxites". Fox and the Whigs supported the American colonies against George III; for that matter, they supported almost anything against George III, for their principal tenets were constitutional government, protection of civil liberties and distrust of anyone wearing a crown. English politics of this era were tumultuous, vicious, often violent, slanderous and heartily corrupt. Forced to canvass for votes in this repugnant atmosphere, most great ladies of this realm chose to organize polite soirées for the swells or simply wave or throw trinkets from their carriage windows when necessity took them among the madding lower orders.

Not the Duchess of Devonshire. She waded into the midst of the tumult, exhorting from the hustings; lifting tankards of ale or gin with the shopkeepers and their families; kissing babies, women, men, whomever, as long as it got votes; promising to store owners some shopping sprees by her wealthy friends if the votes went Whig. She became more famous as a Whig than as an empress of fashion.

And as she matured, she became an adept negotiator for the Whigs. One of her early, though secret, triumphs was to persuade the spoiled, dissolute Prince of Wales (a friend and fellow Whig) from trying to force the House of Commons to pass an unpopular Bill that would pay all his enormous debts and increase his allowance. This would've been the equivalent of a vote of confidence that the Whigs were certain to lose. Georgiana's turnaround of the Prince, who had resisted the entreaties of everyone else, saved the Whig coalition government so arduously formed by Charles James Fox.

In 1806, still in full cry, helping the Whigs to victory in yet another coalition, Georgiana fell ill with what appeared to be jaundice and died on March 30 1806, at age 49. The grief, particularly among Londoners, was so widespread that the duchess's "body lay in state for five days beneath the gaze of an unending file of mourners".

Mr. Crabb is Letters Editor of The Wall Street Journal

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