In the early 1980s I began working on my first book, a biography of Nancy Mitford. Four of the six Mitford sisters were then still living, Pamela in the Cotswolds, Diana in Paris with her second husband Sir Oswald Mosley, Debo, wife of the Duke of Devonshire, at Chatsworth, and Jessica, always known as ‘Decca’, with her family in California. Throughout my research Pam, Diana and Debo were immensely kind and helpful, all of them possessed of great charm and a slightly idiosyncratic sense of humour. They invited me to stay, gave me access to hundreds of letters, and mined for my benefit lucid memories of their early lives and of their family and friends.