This is the first of Terry Pratchett's wonderful sequence of novels about three witches in the remote mountain kingdom of Lancre. In their first outing they have to deal with kings and ghosts of kings, in a plot not unlike a certain Scottish play. Technically an earlier novel, Equal Rites, comes first, but it's not necessary to have read that or any other Discworld book in order to enjoy this. If you haven't read any Pratchett before, here is not a bad place to start.
Great fun, wise and laugh-out-loud funny, it's a book I warmly remember, even after several readings. The two books that follow - Witches Abroad and Lords and Ladies - are even better, and along with the early Guards books (Guards! Guards! and Men at Arms) probably represent Pratchett's best work.