Christy Hadden is an agent with Division 57.
That is an organization which is a highly secret and very selective member of the American Intelligence community. Hadden, not surprisingly, had never heard of it as virtually nobody else had either but she would eventually become the youngest member of that fraternity. As such she will find she has to prove herself to them over and over again but then again, she needs to prove it to herself as well.
When we first meet her, she is really quite far from being an agent. She is still a couple years away from being an adult. She is 15 years old, attending high school, and pretty much hating her life. She is not cool enough to be one of the 'in' crowd. She does not fit in with the jocks, male or female. She could possibly hang with the nerds but even there she feels an outsider. And there are a few at the school who see her as a delightful foil for their bullying.
Even during an exciting trip to the nation's capital she gets to make, along with a small number of other candidates from different parts of the country, and with it a chance to get away from her troubles, she will not find contentment. She will find murder. And very bad people who want her dead. And FBI agents who order people around like it is their right! She takes exception to all of that, especially the last one.
The whole spying for the country and putting her life continually at risk - that comes later. A bit at a time as told in the various adventures, each showing a bit more of her life as she moves from that 15-year-old near outcast to a highly capable 19-20 year old young woman and agent with the Division.