from the back of the book:
Meet Granny Weatherwax, the most highly regarded non-leader a coven of non-social witches could ever have. Generally, these loners don't get involved in anything, mush less royal intrigue. But then there are those times they can't help it. As Granny Weatherwax is about to discover, though, it's a lot harder to stir up trouble in the castle than some theatrical types would have you think. Even when you've got a few unexpected spells up your sleeve.
SFReviews.net calls it "One of the funniest entries in the whole Discworld series". SFSignal says, "Wyrd Sisters is, perhaps, the best of the early Pratchett novels, and I think it ought to stand up with the best overall."