Serenity Sinclair is a student at the Spy School.
She didn't start out that particular day with the intention of becoming enrolled at the academy that may or may not have an actual name but which everyone refers to simply as Spy School. Her day began like every other one in her 17 years of life - with considerable suffering and the constant danger of even more. When the day ended, though, she would move from having no friends - not being allowed to socialize whatsoever - to having five good looking high school seniors clamoring to get her attention. And to keep her safe and alive.
That last part definitely needs explanation.
When we first meet Serenity, her name - the one she has used all her life - is Karlie and her life with no equivocation sucks. With no sense of exaggeration, she tells us that "I am the maid at my house. I am everything here - the cook the cleaner, the 'do whatever I tell you to, because I hate you'" person. If hate sound extreme, think again. Her stepfather abhors her, her stepbrother is constantly cruel to her, and her mother is the one who 'hates' her. Her crime? Being alive, apparently.
Karlie day-to-day life is misery from the time she wakes up early to make breakfast to the time she is allowed to go to sleep after all chores and clean-up is done. And if she makes a mistake of any sort - and even if she doesn't - she is likely to go without food for a couple of days. She is, understandably, rail-thin.
Okay, moving on from this terrible condition we find Karlie coming into contact with a young man who in turns introduces her to several other young men who are quite happy to pull her from that existence and then to provide protection when trouble follows. And then we find out - as she finds out - that for reasons you need to read to understand, her hating mother is not her biological one and her real father is the head of the Spy School she will go on to attend, a man named Michael Sinclair, and he has been searching for her for years and other people want very much to see her dead and that is just the beginning.