Brooklyn is the protagonist of City Spies and the character who experiences the most growth throughout the novel. In the beginning, Brooklyn, whose legal name is Sara Maria Martinez, is a girl who possesses striking hacking abilities and wits, but who also struggles to control her temper and dislikes the idea of being vulnerable in front of others. She refuses to show her softer side and wants to present an aura of strength at all times. Being moved around from foster home to foster home since she was seven, Brooklyn has little experience of home and finds solace on her outdated laptop. She uses it to fight for Justice by hacking into the juvenile justice system to expose her foster parents’ crimes. Instead, Brooklyn is seen as the Criminal until Mother steps in to save her. Despite Brooklyn’s difficulties in trusting others, she senses something genuine about Mother, and decides to take the risk of going with him. This proves to be the first in a long series of risks and changes that Brooklyn forces herself to go through in order to grow and become a stronger version of herself.

When Brooklyn first joins the team, she undergoes a series of tests designed to prove she is capable of being a spy.