Classics, modern fiction, non-fiction and more. Written for secondary and adult students the Oxford Bookworms Library has seven reading levels from A1-C1 of the CEFR. I don't know that you have done anything wrong,' Miss Hepplewhite said. 'But it is possible that you have done something rather dangerous.' William and Susie thought they were just playing a game when they cooked a witch's brew in the old barn and said a spell over it, but Martha was not so sure. And indeed, the three friends soon learn that they have called up something dark and evil out of the distant past.