EARWIG AND THE WITCH. Diana Wynne Jones

Everyone knows that orphanages are horrible places. But Earwig has a surprising amount of power over everyone else at St Morwald’s Home for Children, and loves it there. So the last thing she wants is to be sent to live with the very strange Bella Yaga…Earwig was left at St Morwald's as a baby. Unlike the other children, she loves it there, mostly because she has the run of the place and seems to be able to persuade people to do as she wants. Then one day Earwig is chosen to live with a very strange couple: Bella Yaga, her new 'mother', is actually a horrible witch. Earwig will need all her ingenuity (and some help from a talking cat) to survive…