The story begins with Martina, a young girl from a humble background, receiving an official letter at her family's secondhand clothing shop. To her immense joy, she has passed the civil service examination, a feat rarely achieved by commoners due to the demanding knowledge required and the financial barriers to education. Her father, who had encouraged her to take the exam believing she would fail and thus give up her obsession with books, is stunned and overwhelmed by her success, as he dotes on her and dreads her leaving home. Martina, however, is ecstatic, her primary motivation being access to the Royal Library.
Weeks later, Martina attends the civil servant induction ceremony. Her presence as a commoner who achieved a perfect score on the exam, at the young age of fifteen, causes a stir among the veteran officials. She is assigned to the Ministry of Internal Affairs, specifically the Bureau of Civil Affairs, a department responsible for coordinating various governmental functions.
Upon arrival, Martina is introduced to her fellow new recruits, Sylvian, a proud nobleman who disdains commoners, and Nadia, a sharp-witted woman who values merit over status. Their senior officer, Roran, a pragmatic individual from a viscount family, attempts to instill the principle that rank and status are irrelevant within the civil service. Sylvian immediately clashes with Roran and the others, clinging to his aristocratic superiority. Nadia, on the other hand, quickly forms a bond with Martina, impressed by her perfect exam score. Martina, initially intimidated by the nobles, finds solace in Nadia's acceptance and Roran's approachable demeanor.
Martina's exceptional memory, where she never forgets anything she reads or sees, is quickly apparent. Roran, initially skeptical, is astonished when Martina flawlessly recalls details from a thick list of knights, including their skills, magical attributes, and personalities. He assigns her the task of reading various documents to familiarize herself with the kingdom's operations, a task Martina eagerly embraces.
Her first day concludes with a visit to the Royal Library, her ultimate goal. She is greeted by the librarian, Sophian, who is charmed by her passion for knowledge and offers her a book. Martina, having read all the books in the commoner's library, is thrilled to discover new material. However, her visit is cut short by the closing time, and on her way back, she has an unpleasant encounter with Sylvian, who insists she address him as "Sylvian-sama" and reminds her of her commoner status. This encounter leaves Martina feeling disheartened, but she resolves to focus on her work and friendships.
Later, Roran finds Martina at the dormitory mess hall and, noticing her subdued mood, deduces that Sylvian was the cause. He advises her to maintain distance from those with strong aristocratic leanings for her own peace. Martina expresses her desire to befriend her colleagues, and Nadia joins them, revealing her own dissatisfaction with her family's rigid adherence to tradition and her ambition to prove her worth through her career.
A week into her service, Martina and Roran are dispatched to the First Knight Order to discuss a proposed reduction in patrol budgets, a consequence of declining monster activity. During their meeting with the Knight Commander, Cedric Lambert, an injured knight bursts in with dire news: a mysterious black mist in the eastern forest is spawning large numbers of monsters, including boars, fire-wielding creatures, and wyverns.
Martina, drawing upon her extensive knowledge from various books, immediately offers critical insights into the monsters' weaknesses and optimal combat strategies, astonishing both Lambert and Roran. She correctly identifies a formidable creature as a Sand Crab, a desert dweller, and proposes a plan to exploit its weakness to water. Her detailed knowledge of monster lore, including the properties of a plant called Yuruka, impresses Lambert so much that he requests her direct involvement in the field.
Despite her lack of physical training, Martina agrees. She accompanies Lambert and a contingent of knights to the eastern forest. There, she theorizes that the black mist might be a "miasma pool," a phenomenon described in ancient texts as a source of endless monster generation. She explains that such pools were eradicated during a "world purification" event a thousand years prior, which involved the summoning of a saint. While the immediate threat is contained by defeating the spawned monsters, the underlying problem of the miasma pool remains. Lambert recognizes the gravity of the situation and decides to bring Martina back to the palace to report to the King, acknowledging that this is a kingdom-wide issue requiring a comprehensive solution.
