Though it seems to begin as an affectionate memorial to his maternal grandparents, a testimonial to a rare and perfectly happy marriage, Their Promised Land by Ian Buruma has a deeper purpose. The cache of letters to and from Winifred (‘Win’) and Bernard (‘Bun’) Schlesinger is the pre-email, daily correspondence of two people who could not bear to be apart, yet were separated for years at a time by both world wars.