Kiki Strike Inside the Shadow City by Kirsten Miller
It's a little difficult to fully explain this book, but basically...
Take a group of renegade girlscouts dressed as ninjas, an exiled Eastern European princess, some opium dens and theives liars, a horde of old, an entire city located underneath New York City's subways, and millions of murderous rats. Holding it all together is the very mysterious, and possibly dangerous, Kiki Strike. But who is this Kiki Strike? Is she a Defender of the Innocent? Or an International Assassin? Or possibly a Kung-Fu movie star?
This is an exciting and, well, just plain awesome adventure that features a group of girls kicking ass and taking names. Most wonderful. My favorite is the end of each chapter, which offers helpful hints on such things as how to best follow someone, how to lie, how to spot a fake diamond, how to disguise yourself and how to escape from kidnappers. I can't tell if this is going to be a series or not, but I certainly hope so.
Also, I need an "I am Kiki Strike" t-shirt. I know that Bloomsbury gave a few out, and if anyone's reading this, I WANT ONE!
Be sure to check out the website as well! There's a quiz to decide which irregular you are AND you can download a buddy icon. (Even though I'm a Ananka, Oona was my favorite and she just replaced Colin Firth as my buddy icon. If you don't know me, replacing Colin Firth is REALLY BIG DEAL.) Also, Ananka's blog with her continuing adventures is great. I want to go to Paris now!