Terry Pratchett takes Shakespeare’s Macbeth and then turns it up ’till the knob comes off. It’s all there – a wicked duke and duchess, the ghost of the murdered king, dim soldiers, strolling players, a land in peril. And who stands between the Kingdom and destruction? Three witches. Granny Weatherwax (intolerant, self-opinionated, powerful), Nanny Ogg (down-to-earth, vulgar) and Magrat Garlick (naïve, fond of occult jewellery and bunnies).