In the Tate Gallery there is one of the most beautiful and famous fairy paintings  in the world - The Fairy Feller’s Master-stroke by Richard Dadd. Like all of Dadd’s paintings, it’s loved for its glorious whimsy and exquisite detail, however, its background is far from sweet. This is a case where art history meets gruesome true crime, and we learn that even luminous beauty can grow from dark and sinister soil