The story picks up with a young boy receiving a paper slip from a smiling girl, which causes him immense shock. The girl declares her victory and disappears into an alley, leaving the boy bewildered and clutching the paper.
The narrative then shifts to the Roland Kingdom, a 300-year-old nation founded by the hero Abel Roland. The kingdom is depicted as prosperous and patriotic, fiercely defending itself against the expansionist Diagilev Empire. This history sets the stage for a grand 300th-anniversary celebration at the royal castle, which also serves as a veiled event to find a bride for the second prince.
Among the attendees are Prince Edward Roland, the first in line for the throne, known for his ideal prince persona, and Juliana Louis, the daughter of a loyal marquis family, renowned for her perfection and grace. Despite their prominence, they do not dance together.
Later that night, Juliana, tired of her public persona, leaves the ball. She is revealed to be a master of disguise and acting, a skill honed from childhood to entertain her ailing brother. Her father, the Prime Minister, tolerates her escapades due to the valuable information she gathers.
Two days after the ball, Juliana receives a summons from Prince Edward, which she dreads. She views him as a superficial actor, a "third-rate performer" hiding behind a mask of kindness. Despite her reluctance, she accepts, acknowledging her duty as a marquis's daughter.
Juliana arrives at Prince Edward's office, where she meets him, his aide Silas Inglott, and the captain of the third knight division, Kiel Maybrick. Edward, shedding his "ideal prince" facade, reveals he believes Juliana is "Ria," a girl who defeated him seven years prior. He presents a crumpled "one-time favor" ticket signed by Ria. Despite Juliana's denials and the lack of physical resemblance, Edward insists, citing a handwriting analysis that matched her writing to "Ria's." He demands she become his "pawn."
Juliana, realizing she has no choice and that her father has already consented, agrees to become his pawn. She is tasked with infiltrating the Royal Capital Church to gather information on a potential Sabbath and the profits from "indulgences." Edward emphasizes that she will operate independently, using her own skills.
Juliana, embracing her role as a pawn, devises a plan. She adopts the persona of "Eren," a clumsy, devout, and slightly ditzy apprentice nurse, to infiltrate the church. Her loyal maid, Marie, assists her in this endeavor.
Eren's infiltration begins with a dramatic, clumsy entrance at the church gates, drawing attention and establishing her persona. She quickly befriends fellow apprentice nurses, Ann and Millia, and navigates the church's daily routines, all while secretly observing and gathering information. She discovers a suspicious hidden passage within the church and encounters a high-ranking priest, Michael, whom she suspects of corruption. Michael, initially wary, sees Eren as a potentially useful, albeit clumsy, pawn.
Marie continues to provide intelligence, confirming the possibility of a Sabbath and the involvement of church-affiliated nobles. Juliana, as Eren, plans to infiltrate the suspected Sabbath location. Meanwhile, Silas, Edward's aide, is deeply concerned about Edward's reckless actions and the potential repercussions of his obsession with "Ria." He worries about the consequences for Juliana and the Louis and Olcott families.
Juliana, in her role as Eren, continues her investigation, discovering a hidden passage and a suspicious priest. She also learns that her father, Gerald Louis, a staunch patriot, has already given his consent for her mission, much to her exasperation.
The narrative then delves into Edward's past, revealing his arrogant and manipulative nature, which was only temporarily softened by his encounter with "Ria." His obsession with finding Ria has led to his current actions, much to the dismay of his childhood friends, Silas and Princess Sherry.
Juliana, as Eren, successfully infiltrates the church and begins her investigation, while also dealing with the challenges of her new identity and the suspicions of those around her. The story ends with Juliana preparing to attend the potential Sabbath, setting the stage for further intrigue and danger.
