Gaia Moore is a loner with a don't-give-a-shit attitude. Her life is dangerous and people who get close to her tend to get hurt. She thinks of herself as a freak because she is genetically fearless. In reality, she is actually quite pretty, incredibly smart, and very unique. Her father trained her to be a fighter so she would be able to defend herself when she got into dangerous situations. But since nature compensates, she also has an amazing adrenaline that she can use in fights. It has consequences, though; she blacks out for a few seconds.

Her mother was murdered when she was 12 years old and her father, Tom, left that night. He felt that it was his fault that his wife, Katia, died because he is in the CIA and it had a slight role in her death. Five years later, the first book begins, and we start to hear from Tom and find out that he still loves Gaia - and writes her letters every day, only to lock them in a drawer, unsent. George and Ella Niven are Gaia's foster parents. George used to be Tom's mentor when Tom was younger and just starting out in the Agency. Little does Gaia know that George is still in contact with her father so he can keep up with how she's been doing. Ella is the wicked stepmother and we find out later that she is not who she appears to be.

Ed Fargo is an ex-skate rat. He ended up in a wheelchair after an accident that left his lower body paralyzed. Heather Gannis is the most popular girl in school. She is the leader of the FOHs (Gaia's way of referring to the Friends of Heather). Sam Moon is the hot college guy that Heather goes out with. And there is another character, Loki. It isn't possible to explain more about him without spoiling the series, or at least the first few books.