The second half of The Clocktaur War -- and really it's one book, read them together. And SERIOUS spoilers ahead.
It opens, of course, with their arrival at the city. They find they have to sneak Grimehug into the inn; no one will take gnoles. Grimehug tells them all he knows about clocktaurs -- not enough -- and so they have to deal with getting to the belfrey of a cathedral, a Grey Church that is no such thing, some footpads in an alleyway, a woman who is flattered by Learned Edmund's admiration of her indexes, chicken drawings, Caliban and Slate's being awkward with each other for a long time, and more.