This book is set mostly in the region of Überwald, land of dwarves, vampires, and oh yes, werewolves. This is also the land where premium fat mining takes place, and is therefore of prime importance to Ankh-Morpork. The crowning of the dwarven Low King is about to take place, and Vetinari decides to send, as ambassador, newly-made Duke Vimes. Who is less than happy with the situation (though Lady Sybil is thrilled.)
To complicate matters, the Scone of Stone (necessary for the investiture) has been stolen, as has a plaster replica; Angua's brother, also a werewolf, has started a movement to take over Überwald; some dwarves are very unhappy about the "licentious" behavior of Ankh-Morpork dwarves, particularly the fact of females dressing up as females (all dwarves are bearded and most think the very concept of female should be private); and here comes undiplomatic Vimes, with a troll and obviously feminine dwarf in tow. Which, of course, could be exactly what is needed to get to the bottom of the mystery.
I felt that this book was a little less focused than some of his previous efforts. He does, however, set the mood exceedingly well; I think that you could read this book on a sunny day and become convinced that it was overcast outside.