The Gallagher Academy is the main setting of the novel. On the outside, the school looks like a normal mansion, but inside, laboratories, subbasements, and secret passages allow Cammie and her friends to conduct research and sneak off school property. During the Code Red in the early chapters, the school uses built-in technology to hide evidence of spy activity, turning the academy into the elite boarding school its formal name suggests. Retinal scanners to enter classrooms and specific languages/dialects to be spoken at lunch show how, even outside of class, the girls never truly stop training.

Carter weaves real history around the one created for the school. The Gallagher Academy was founded by the fictional spy Gilly Gallagher, famous among spies for stopping an assassin no one’s ever heard of from killing Abraham Lincoln. Her sword rests in the academy’s main hall and is the school and Gallagher family crest. Gillian represents the ingenuity of women and, specifically, how the sisterhood bands together to better technology and intel collection. Things like duct tape are attributed to the Gallagher girls, as well as discoveries like how no two sets of fingerprints are the same. By building and re-appropriating history into the Gallagher world, Carter grounds the novel in the real world while still having it be strictly fiction.