Whenever the possibility of a film version of a difficult or complex book is mooted, speculation mounts about how it will be done. Usually at this point some dull spark will pipe up that some novels are simply ‘unfilmable’ (though such reservations are sometimes shared by the authors of the novels in question: David Mitchell himself never believed that his novel Cloud Atlas could be turned into a movie: ‘My only film-related thought when I was writing the book was what a shame that no one would ever, ever film this,’ he said.