You know this story. A faithful retainer, egged on by his murderous wife, kills his king. There's three witches, of course, and ghosts, and some good old-fashioned Shakespearian verse.
Of course, this time we're in the Discworld, so things get a wee bit twisted...
For example, there's Nanny Ogg, a witch of many marriages, absolutely no morals, and a fondness for drink. And her hedgehog song. Then there's Magrat Garlick, a dreamy New-Age type witch who believes in the sovreign power of herbs and romantic eyeshadow. And there's always Granny Weatherwax, who "can't be having with that sort of thing." Add in a Fool, a band of traveling players, a disguised heir, a land that cares if the king cares for it, and some interesting godmother gifts, and you have a recipe for Discworld havoc.
Which is all to the good, of course.
Pratchett had really hit his stride by this point in the series. This one feels like full-fledged Discworld, right down to the phrasing ("Magrat wore a startilingly green dress that would have been revealing and clinging if Magrat had anything to reveal or cling to.") Not a bad place to start in a series where you can start in the middle and work out toward both ends.