SOLVED. Children/ YA Adventure - Group of girls are solving a mystery of rats in the New York underground. [s]

[Carolin]

I've read this book around 2009 and I always thought it is from Chris Riddell, but the closest match of his works is 'Ottoline', but the plot is not like the one I remember.

It is a book about a group of girls in New York and one of the girls is very mysterious, who lives without parents and has a very specific skill set, like picking locks or something. At the end of the book she vanishes, but reassures the others she will come back when needed or something like this.
I'm pretty sure that at first, they are trying to solve some sort of mystery/riddle, like a missing person or object, but the clues are leading into the New York underground, where they meet a lot of malicous rats. They deal with the rats with some kind of sound machine. The sound machine is build by one of the other girls, who is like a inventor or something? I remember there being very little adult super vision, apart from maybe one grandparent or so.
At the very end it is fore shadowed that while the rats are defeated, the deaf ones are immune to the sound machine and grow stronger?

[Becca]

Inside the Shadow City by Kirsten Miller, the first book in the Kiki Strike series?

[Carolin]

Yes!! As far I can gather from the description thats the right book :) Thank you very much!!!

For the mods:
This is solved! Inside the Shadow City

[Kris]

Glad you found your book, Carolin.

"Kiki Strike" series by Kirsten Miller - https://www.goodreads.com/series/4292... - Becca's find.