Sarah Hilary and Sabine Durrant join Joe Haddow for a Book Off! They chat about their new novels, choosing their settings, 'chalk n cheese' detective duos and balancing darkness and light. Sarah's book ('The Drowning Place') has ghostly elements to it, so they discuss ghosts and whether the authors believe in them... THE BOOK OFF 'The Mahe Circle' by George Simenon VS 'Your Blue-Eyed Boy' by Helen…