'Elizabeth Jane Howard is one of those novelists who shows, through her work, what the novel is for .... She helps us to do the necessary thing - open our eyes and our hearts'rn-Hilary MantelrnrnIt is the 1950s and as the Duchy, the Cazalets'beloved matriarch, dies, she takes with her the last remnants of a disappearing world - of houses with servants, of class and tradition - in which the Caza…