Kiki Strike:
Inside the Shadow City
by Kirsten Miller
Bloomsbury Children's Books, 2006
This is the first book in the Kiki Strike series. It is a mystery/action adventure novel for older children and young adults, with the protagonists themselves ranging from about 12-14. It is primarily written for girls, but not in a princesses and fashionista sort of way. Despite the princesses and the bits about fashion. Seriously, boys will enjoy it too.
Ananka Fishbein is a 12-year-old history nerd; this would make her an outsider at most schools, but thanks to a bequest from her very odd grandfather (he's dead, but he'll be making an appearance later), she is also attending an exclusive private school in New York City. Poor(ish), weird, and smarter than your average tween, she is not one of the popular kids.
Which bothers her sometimes, but from the age 12 on, she also happens to be involved in international assassination plots, local kidnappings, and at least a hundred years worth of smuggling rings, so the school stuff doesn't bother her too much. Usually.
The center of these various adventures is the mysterious and elusive Kiki Strike. About 12 years old, small for her age, and surprisingly capable across all domains, Kiki has plans for Ananka. Unfortunately, almost anything else I could say about her would be a spoiler, and/or false, and/or true but not in the way you think. She's that kind of person. Ananka is useful to Kiki both because she knows a ridiculous amount of NYC history, and because she has discovered an entrance to the Shadow City, an underground city used by untold ancient smugglers, thieves, and ne'er-do-wells of all sorts. While now abandoned, it would be a valuable resource to anyone who wanted to rob, explode, explore, subvert, or poison significant parts of the city without being detected by the authorities. Or, you know, whatever.
Anyway, many unlikely and adventurous things happen. Fake kidnappings, real kidnappings, treasures lost and found, devious contraptions constructed, critical infrastructure critically damaged, and at least one royal family either destroyed or protected, depending on your viewpoint.
This is a fun book, with a lot of real history, a lot of truthy history, a ton of adventure, and a lot of spycraft. It is written for teenagers, which in this case means fast-moving and often over-the-top, with a bit too much drama. Some of the villain show-downs sound more like middle-schoolers arguing than grown adults (but then, some of the villains are middle-schoolers, and all of the heroes are). The story is interrupted by sections of a spy-manual written teenagers; not bad stuff, but it definitely throws off the pacing. But even so, it's a fun, often silly, high-energy action story, and is one of the better spy adventures written for teens, and one of very few that star an (almost) all female cast.