What is the main conflict in Only the Good Spy Young by Ally Carter?

This novel for teens, primarily young women, is the fourth in a series about trainee spy Cammie Morgan. In this entry, Cammie finds herself the target of kidnapping attempts, taking the lead in missions to retrieve important information and drawn further into her complicated relationship with cute fellow trainee spy Zach. As it builds to an explosive climactic confrontation between Cammie and operatives of the evil Circle, the narrative also explores themes related to friendship and loyalty, identity, and the tension between entrapment and dreams of freedom.