An unseen world lives behind the fog and clatter of Victorian London. A secret network of female spies operates with quiet precision, solving puzzles that polite society pretends not to notice. Seventeen year old Mary Quinn steps beyond the limits placed on girls of her era when she joins this clandestine circle, receiving training in observation, disguise, and the art of moving unseen through parlors and markets alike. The Agency teaches its members to read rooms, to follow lines of sight others overlook, and to turn ordinary moments into opportunities for truth. Mary embraces the challenge and discovers that courage is not loud, it is practiced. The narrative pays careful attention to historical detail, letting readers from Canada and the United States feel the steam, the smoke, and the bustle of the city as if they stood there themselves. The plot threads weave together as Mary navigates class expectations, emerging technologies, and the delicate politics of power, all while quietly testing loyalties, and facing hazards that could change her future or erase her name from the ledger of the living. The central question asks how a young woman can carve a place for herself when the rules insist she stay quiet, and how a seeker of truth can stay true when every answer could betray a confidant. The pace is brisk, the scenes vivid, and the tension between trust and deception never stops building. This is the opening volume in a trilogy, and the second part is anticipated with the promise of more peril, more discovery, and deeper ties to Mary’s evolving identity. Critics praise its atmosphere, its momentum, and its commitment to historical authenticity, and Candlewick Press offers a high rating that signals broad appeal and reliability. North American readers who enjoy historical mysteries with a bold heroine will find this a compelling entrance into a past that feels immediate, alive, and dangerously relevant. For fans who crave stories where deduction meets character and consequence, the book opens a door to a world where every clue matters and every choice leaves a mark on the future. Rating 4 out of 5 by Candlewick Press.