Magic is real. History is a big, fat lie.
Hyacinth Hayward’s mother has just been kidnapped by lumpy gray monsters in post office uniforms. But why? Well, before Hyacinth moved from Illinois to London, she read up on the city’s history. Too bad for her. Because the books are wrong. The truth is, London was built on magical rivers, and all the major events in its past have been about people trying to control the magic. And her family is somehow tied to it.
In the chase to get her mom back, Hyacinth encounters a giant intelligent pig in a bathing suit, a boy with amnesia, an adorable tosher (whatever that is), a sarcastic old lady, and a very sketchy unicorn. Somehow Hyacinth has to figure out who to trust, so she can save her mom and, oh yeah, not cause a second Great Fire of London.