There has never previously, I believe, been a novel about Margaret Cavendish, Duchess of Newcastle, one of the 17th century’s foremost female authors, philosophers and eccentrics. But there have been several near misses. Virginia Woolf’s Orlando tips its cap to her: Orlando, just like Cavendish, is a feverishly imaginative, androgynous aristocrat afflicted by the ‘honourable disease’ of writing, filling folios with the speed of an addict.