Aristocrats focuses on family drama. At 19, Caroline, the Duke's eldest daughter, eloped with Henry Fox, an ambitious radical politician, and was estranged from her parents. The second daughter, Emily, was married to Lord Kildare at 14 and settled in Ireland, producing 22 children - some of them by their siblings' tutor, William Ogilvie, whom she married on her husband's death. Louisa was fixed up by Emily with the horse-mad Tom Connolly, the richest man in Ireland; childless, she spent much of her time refurbishing Castletown House and maintaining the role of virtuous wife. When Connolly died, she discovered from his account books that he had been keeping a mistress. Voluptuous Sarah, the fourth daughter, caught the eye of the Prince of Wales when she was 15, was hastily matched up with the impotent (or just uninterested) Sir Charles Bunbury, took several lovers, had an illegitimate child, a scandalous divorce and a late happy marriage to a half-pay captain called Napier. Her three Napier sons became famous generals.
The stories are recounted with a good deal of feeling, thanks to frequent quotation from the lifetime's correspondence of the four women, who modelled their letter-writing style on the warm sensibility of Madame de Sevigne. Caught up in the family romance, they wrote copiously and lovingly of themselves, their husbands and their children, with outpourings of affection ('My beloved, adored sister. My heart still beating with the agitation that the sight of your dear handwriting gave me this morning') and ecstasy ('Henry naked is the dearest little being on earth') and sublime self-confidence ('Pray now who the devil would not be happy with a pretty place, a good house, good horses, greyhounds etc for hunting, so near Newmarket & pounds 2,000 a year to spend? Add to this that I have a settled, comfortable feel'). The letters contain endless small conspiracies ('Don't say I said so, but . . .') to conceal, for instance, how dull they think Louisa's husband is. Later, the deceptions become more serious when government censors take an interest in Emily's son, Edward Fitzgerald, leader of the United Irish, on the run in 1789, and when Louisa and Sarah have different attitudes to the rebels.
A family saga offers plenty of scope for digression. As well as some grand set-pieces - the busy River Thames, Vauxhall Pleasure Gardens, the staff of a great house - Tillyard provides informative and evocative pictures of medical practice in Bath, where Caroline administered the toxic concoctions of fashionable quacks to her sickly two-year-old (her favourite child, who grew up fat and subject to fits - another topic not to be mentioned in letters), and of the free-and-easy atmosphere of Holland House, always full of indulged children, card-playing, gossip and political intrigue. There are descriptions of the family's portraits, by Reynolds, Ramsay and Batoni, and their favourite authors - Voltaire, Rousseau, Thomas Paine. Above all, there are the vivid glimpses: of a footman's livery; of shopping; of the tedious preparations for inoculation; of childbed and dying; and of the nitty-gritty of a European tour. In 1776 Caroline, suffering badly from her period, was carried in a sedan chair over the Alps: 'Only think, sweet Cis,' she wrote to Emily, 'I was unluckily out of order just the day I passed Mount Cenis.'
Sometimes the author's preference for empathy over analysis runs away with her ('The wedding night, the slippery loss of virginity in the flickering candle-light, had terrified her'), and she occasionally fails to escape the fell hand of Georgette Heyer ('At the age of 18, Caroline Lennox was a plump, nervous girl with hurried, wide-open dark-brown eyes . . .'). But it is, after all, only recently that the lives of women such as these, and their views on interior decoration, childrearing and infidelity, have been considered fit subject-matter for history books, and it is still difficult to get the tone right. At its best, however, Aristocrats succeeds in using the insights of the novel to provide a rich portrait of the age.