"The Fifth Elephant" by Terry Pratchett

Plot summary: Someone stole the Scone of Stone (the traditional dwarven throne) so the dwarves can't crown a new king. Sam Vimes gets sent as Ankh-Morporkian ambassador to Überwald, the ancestral home of most of the Discworld's non-humans, for the coronation, and he can't help investigating the theft. Captain Angua disappears from Ankh-Morpork because her family (of werewolves) are up to no good again, and Captain Carrot (her love interest) follows her because he doesn't know why she disappeared. While the Watch's entire upper echelons are off in Überwald, Sergeant Colon gets promoted to Acting Captain and promptly makes such a mess of the Watch that practically everyone deserts.

(I think that's the longest plot summary I've ever done for one of these. This book's plot is kind of all over the place.)

Sergeant Detritus is becoming one of my favorite Watchmen, and I'm not sure why. He's not very intelligent, but he's a very straightforward kind of not very intelligent, and he can be quite cunning at times. Plus he's endearingly nice. And as a troll, his intelligence scales with how cold it is (something to do with Discworld trolls having silicon-based brains), which means in the colder climate of Überwald he's quite smart.

Were this a videogame, I'd rate it: T15+ for crude humor and swearing. This one almost feels like it would turn out as an open-world game of some sort.

3 stars.

Favorite lines:

    "Sometimes," Vetinari said, testily, "it really does seem to me that the culture of cynicism in the Watch is... is..."

    "Insufficient?" said Vimes.

    Page 23.

    *As a member of the dead community, Reg Shoe naturally thought of himself as an ethnic majority.

    Page 81. Reg Shoe is the Watch's only zombie officer.

    [Vimes addressing an Igor]

    "Sorry," he mumbled. "I thought you were Igor."

    "Oh, you mean my couthin Igor," said Igor. "He workth down at the embathy. How'th he getting on?"

    "Er... he's looking... well," said Vimes. "Pretty... well. Yes."

    "Did he mention how Igor'th getting on, thir?" said Igor, shambling away so fast that Vimes had to run to keep up. "Only none of uth have heard from him, not even Igor, who'th alwayth been very clothe."

    "I'm sorry? Is your whole family called Igor?"

    "Oh yeth, thir. It avoidth confuthion."

    Pages 231-232.

(Endnote: I didn't know until after I'd finished reading this that there was a famous movie (i think) called The Fifth Element. Suddenly, the title was a lot funnier to me.)