If we are to believe Agatha Christie, then the author was not at all like her creation Miss Marple, the spinster sleuth of St Mary Mead: ‘I never can see why anybody thinks that I resemble Miss Marple in any way,’ she once complained. Instead, Christie – who was born 134 years ago this week – felt that she was much more like her recurring character Ariadne Oliver, an apple-munching writer of crime fiction who despaired of making her most famous detective a Finn (Christie’s own Hercule Poirot was proudly Belgian), and whose complaints often mirrored those in Christie’s own...