“As I dropped, my mom’s words flashed through my mind: Wherever we’re together, it’s home. I was finally on my way to get Mom back, and in some strange way, it felt like I was going home.”

I immediately knew that Hyacinth and the Secrets Beneath by Jacob Sager Weinstein was likely to be a GU story just from the title. Not only a titular girl, but a reference to the underground (like these)! It also happens to be the third GU book I’ve encountered which is set in a magical version of London (the others being Un Lun Dun and Neverwhere).

Hyacinth, 12, comes to spend a summer in London with her flaky, distracted mother, who grew up there. One day she innocently attempts to merge the separate faucets for hot and cold water and things turn weird – a magical drop of glowing water escapes, and monsters made of dirt appear and kidnap her mother in order to force Hyacinth to recapture the drop before it causes too much trouble. Fortunately, an old lady who lives in the building seems to know all about this strange magical water and helps Hyacinth, leading her underground where secret magic rivers flow beneath the city (unfortunately for Hyacinth, mostly through the sewers).

SPOILERS They make good progress, even avoiding a dangerous boy and giant boar, and have found the drop and are close to finding Hyacinth’s  mother, when everything is turned on its head. In one of the most severe companion betrayals I have encountered, the old lady is revealed to be the Adversary, and Hyacinth discovers that the monsters weren’t really all that bad, and the boy and boar were not dangerous and in fact become her new companions. Now she must stop the lady from gaining more power and possibly destroying the world, which also entails rescuing her mother (whose blood is a crucial ingredient in a dark spell). The final showdown, often a magical battle, in this case also involves a knife fight.

Looks like there’s already a sequel coming out with a new adversary for Hyacinth.