Troll Tales: Whimsical Wonders of Discworld

It's a fiction fantase book. Some kind of Terry Pratchett style - funny and nice. There should be a water tower where people could live for a while so there should be a place for them. And I have two main characters. First one is a killer, second one is a girl. The killer is a kinda teacher for her, no romantics. I want them to be like silhouettes. The water tower is in the forrest. Colors - more like dark blue. No hats, no river, no buildings.