Bridget Wilder is an agent for Section 23.
That Section (not sure if there are other numbered sections ... there sort of has to be right, because being #23 without there being or having been #1-#22 seems sort of goofy) is part of the CIA. Except apparently the CIA does not know about it. We are told it is "a covert agency buried deep inside the bowels of the CIA" which is kind of cool and a whole lot of spooky.
But Wilder is not a spy, really. Well, she is and isn't and that is what makes the adventures about her really neat in a really confusing sort of way.
"It's about an unnoticed, underestimated 13 year-old girl who finds out that her biological father is a legendary spy of international renown and fearsome reputation. She also finds out that her existence is as much of a shock to him as his is to her. He wants to get to know his daughter and decides the best way to do that is to get her involved with the family business, i.e: spying. He kits her out with all manner of cool gadgets and weapons that make her super-fast and agile, that give her the ability to decry when people are lying, and that allow her to shoot laser beams from a tune of lip balm. Bridget displays a real aptitude for spying. Which is good news because she's about be plunged into a world where no one is what they seem and nothing anyone says or does can be trusted."
That's the really neat part of the series. The really confusing part is that Section 23 is filled with a bunch of poop-heads who are out to cause trouble and that makes trouble for Wilder and her father, who has the nifty name of Carter Strike. But when people say that Strike is legendary, they say it because he is really awesomely good at it and with some training so is Wilder so those poop-heads at Section 23 - and other poop-heads to come later - learn that the hard way.