Sister in arms

"Mad, bad and dangerous to know," Lady Caroline Lamb's famous diary description of Lord Byron, is amply justified by this vivid…

"Mad, bad and dangerous to know," Lady Caroline Lamb's famous diary description of Lord Byron, is amply justified by this vivid biography of his half-sister. His adulterous, incestuous affair with Augusta Leigh ruined her life. The poet was so promiscuously seductive that romantic Georgian ladies found it difficult to remain upright in his company. Augusta, five years his senior, evidently did not even try to. Her biographers call her "warm-hearted, easygoing, generous," gay, impulsive, lacking judgment and stubborn, with a "genius for doing the wrong thing at the wrong time".

English high society late in the 18th century was extravagantly prolific, yet exclusively introverted. Families habitually intermarried, cousins often married cousins, to retain and augment inherited wealth. Many married women were expected to give birth annually as long as possible and managed to take lovers in between confinements.

Michael and Melissa Bakewell provide three relevant family trees, the Byron Descent, the Holdernesse Descent and the Trevanion/Byron Connection, which are so widely extensive and intricately self-referential that even the people dependent from the intertwining branches must have been perplexed occasionally by their genealogical status. One can imagine rakish house-parties in which absent-minded relations cavorted in shared gene-pools.

The adultery and incest in which Byron and Augusta often indulged over a period of several years were not accidental. They knew that they had the same father (the well-named "Mad Jack" Byron), that the poet had a wife called Annabella and that Augusta was married to one Colonel George Leigh of the 10th Hussars, who was complaisant when Byron helped him with his gambling debts.

Leigh was an equerry to the Prince of Wales and a popular member of the royal horsey set until he was caught cheating on livestock sales. While in favour and afterwards, Leigh spent a lot of time away from home, attending race meetings and carousing on the estates of aristocratic fellow gamblers. He was one of society's most convenient cuckolds.

Gambling, the Bakewells write, "had become a national mania. Fortunes were won and lost overnight, sometimes in a matter of minutes, and betting was by no means confined to the turf . . . Lord Barrymore, who managed to run through £300,000 in four years, once bet the Duke of Bedford that he could produce a man who could eat a cat alive - and won!"

As an inveterate loser, Leigh was an erratic and inadequate provider of his family's domestic support. Augusta often depended on royal patronage and the charity of friends. She was fortunate enough to be granted a grace-and-favour apartment in St James's Palace for many years, but was always vulnerable to the vengeful machinations of Annabella. Lady Byron blamed Augusta for Byron's deserting her and then leaving the country.

When it was suggested that he liked children, Byron wrote: "I abominate the sight of them so much that I have always had the greatest respect for the character of Herod." Even so, according to Annabella, he fathered one of Augusta's daughters, Medora, who became another cause of Annabella's hatred.

The biography presents the correspondence between hypocritical Annabella and naive Augusta in exhaustive and exhausting detail, serving more thoroughly than necessary to show one woman's implacability, the other's decline. The story is a false tragedy, having at its centre a villainess but no admirable heroine or hero. However, it helps to explain why Byron chose to go into exile in Italy and Greece. And perhaps the book's most valuable function is that it adds understandable poignance to some of Byron's poetry, especially Childe Harold's Pilgrimage, and, most obviously, the Epistle to Augusta. Byron's madness and badness were fatally dangerous to himself.

Patrick Skene Catling is an author and critic