Samuel Vimes, Commander of the Ankh-Morpork City Watch and Duke of Ankh, thought that things were bad enough when he was forced to go to Überwald, a largely wild territory, on a diplomatic mission. That was before he found himself entangled in a plot to spark the dwarf equivalent of a holy war, not to mention running in the frozen wastelands of Überwald with werewolves on his trail.
The plot concerns the appointment of a new Low King of the dwarfs. It is a controversial choice and the cause of a rift in the dwarf community. Lord Vetinari sends Vimes as an ambassador along with Detritus and Corporal Littlebottom; the idea being trolls and dwarfs are ethnic majorities in Überwald, where the Low King resides. Littlebottom is not a typical dwarf, as she displays being female and even wears a dress, which is highly offensive to conservative dwarf society. Accompanying them as both guard and spy is Inigo Skimmer, a scholarship boy from the Assassins Guild.
Once in Überwald Vimes finds his relationships with dwarfs, vampires and werewolves very different from the ones he experiences back home. He also finds the 'Scone of Stone' (a large piece of dwarf bread the Low King must be crowned on) has been stolen. Perhaps there is a link to the recent theft of a replica of the Scone in Ankh-Morpork, and the murder of a manufacturer of prophylactics in that city. Vimes must use his detective skills to solve the mystery of the Scone, while trying to stay alive. Having Lady Sybil with him is an education for both of them. Sybil sees the Sam Vimes who inhabits a world of criminals and still comes home with a (relatively) clean soul and Sam sees that Sybil is resourceful in the face of danger. After some failed attempts, Sybil finally manages to tell her husband that he's going to be a father.
A sub-plot involves Carrot Ironfoundersson and Gaspode going in search of Carrot's werewolf girlfriend Angua. The simultaneous absence of both Vimes and Carrot from the city watch requires one of the existing watchmen to be promoted. Sergeant Fred Colon is the senior officer, and so is made Acting Captain. Colon is not comfortable being a leader, and deals with the position very badly, becoming excessively strict and paranoid as the Watch crumbles around him.
The novel gives more detail on werewolf society, including the concept of yennorks, werewolves who cannot shapeshift, and are permanently in human or animal form. It also explores the society of dwarfs on the Disc, introducing the 'drudak'ak' (which roughly translates as "they who do not get out in the fresh air much"), conservative dwarfs who are the keepers and interpreters of dwarf law.