Celebrities, we have it on good authority, are like candles in the wind. As it is the nature of candles to illumine what would otherwise be dark, this means that within every biography of a Marilyn or Diana there are also fleeting biographies of the purely tangential, those who are of interest only because they once knew the famous. The longer the afterlife of a celebrity persists, the more famous these members of the support cast will become, until, in the end, they are awarded the highest honour that this second-hand form of fame can bestow - biographies of their own.
Byron, who trailblazed the modern cult of celebrity, has been written about incessantly for almost 200 years, and the allure of his fame still touches those who knew him. Hence, this new book on his half-sister, Augusta Leigh, a woman whom Byron's very first biographer, Thomas Moore, accurately described as being "nothing above the ordinary run", and who did little of note throughout her life. Apart, that is, from sleep with her brother, and thereby precipitate the most spectacular marital bust-up in literary history.
Not surprisingly, everything in this biography leads up to Lady Byron's discovery of her husband's incest, and everything after it has the feel of a coda. Yet although Michael and Melissa Bakewell open with Lady Byron's whispered revelation of the truth about Augusta to a horrified confidante, the story they then have to tell is actually less gothic melodrama than Vanity Fair. Augusta's father, "Mad Jack" Byron, was a notorious spendthrift and rake; her mother was a marquess's wife seduced and then abandoned by "Mad Jack", so that Augusta, like her half-brother, was brought up with the twin inheritance of snobbery and crippling debts. Yet while Byron transcended the seedy milieu into which he was born, Augusta sank ever deeper into it, until, finally, it utterly submerged her.
That this happened was due less to the fallout from her incest than to an earlier and far more serious mistake. Appalling marriages were very much a Byron tradition - even down to his first name, her choice of husband was the image of Thackeray's selfish, debt-laden cavalry officer, George Osborne. Unfortunately for his wife, however, Colonel George Leigh neglected to die heroically on a battlefield, instead allowing his career to be ruined by various financial misappropriations and the subsequent loss of the patronage of the Prince of Wales.
George had a talent for nothing beyond gambling and aggressive self-pity, and the consequence for his wife was a disastrous leeching away of the family finances. Struggling against a nature that was, in the Bakewells' words, "undemanding, unambitious and unselfish", Augusta did her best to shore up her family's eroding status, but it was a hapless effort. Then, just when it seemed her fate to live dowdy and unloved for ever, back into her life came her long-lost - and, by now, fabulously glamorous - poet brother.
The great achievement of the Bakewells' biography is to make us appreciate that Augusta had at least as large a stake in the subsequent affair as did Byron himself. But this is not a lesson that the Bakewells choose to draw. Their Augusta is as passive before the vicissitudes of Byron's marriage as she was later before the deliberate cruelties of a vengeful Lady Byron. It is these same cruelties that compel the authors to admit: "We have done our best to be fair to Annabella [Lady Byron], but to present her sympathetically has proved an impossible task." Which is to be regretted, given that it was brother and sister between them who turned Annabella's heart to stone.
To cast Augusta as an innocent during the terrible months of the marriage is to make Byron seem more selfish - and Annabella more monstrous - than either really was. Above all, it is to make Augusta herself seem too enfeebled. Perhaps as a result of this, the Bakewells do not seem to take Augusta seriously as a muse, yet she helped to inspire not only "Manfred" and "Cain", but also a series of lyrics that are among the most haunting love poems Byron ever wrote. It is not for these that Augusta will be remembered, however, but rather as one of the earliest martyrs to the cult of celebrity, as vivid proof that, while a candle may illumine, it can also consume.
Tom Holland's novel about Byron, The Vampyre, is published by Abacus (£6.99)