Thematically, moral ambiguity is a prominent feature of Brian's work. Extreme cases of loyalty and antagonism are personified in characters such as Noelle Lange and Ivy Slade—to degrees that are sometimes questioned or denounced by the narrator. However, it is often only after the details of another character's background have been revealed that Brennan can understand what motivates them, which will occasionally leave her conflicted in her judgments. The series has companion works, set in the past and the future, which are dedicated to further exploring character. These novels include the "Private" prequel collection, which focuses on various figures, and the spin-off series "Privilege", which follows the resourceful but disturbed Ariana Osgood.