The Grim Grotto by Lemony Snicket

The eleventh book in this series leaves the children underwater in a submarine, looking for the sugar bowl and on its way to the Hotel Denouement for a VFD meeting. They meet someone who studies fungi and are forced to consider that the world is not easily divided into villains and heroes. There's some good poetry. Finally the book hints that by its end the Baudelaire children have broken out of the cycle in which they've been trapped.