What metaphors are used in Only the Good Spy Young by Ally Carter?

In many ways throughout the narrative, Cammie's attitudes, actions, and reactions are defined by her feeling of being trapped, both by the mysterious desires and ambitions of the Circle and by the desires of those around her to protect her from those desires and ambitions. She is constantly watched over by, and has her actions essentially controlled by, her parents, her friends, her teachers, and what amounts to the entire international espionage community. It's important to note, however, that other characters also have experiences of being trapped. These include Joe Solomon and Zach Goode.

As previously discussed, this theme is metaphorically evoked in the experience of the ravens in the Tower of London or birds trapped within the Tower's ancient walls and whose disappearance would herald the downfall of England. There is the implication throughout the narrative that if Cammie disappeared, the entire espionage community would, for some mysterious reason, experience a downfall of its own.