Dalian, the guardian of the forbidden Bibliotheca Mystica de Dantalian, takes advantage of a period of calm following the events of the main series to enroll in a prestigious girls' school. There she meets Priscilla, an impoverished aristocrat's daughter, and the two are drawn together by a mystery concealed within the school. As they work to solve it, Dalian experiences everyday school life for the first time. Despite her sharp and often rude demeanor, she gradually forms friendships with her classmates Priscilla, Cecil, and Margaret. The story focuses less on the supernatural incidents involving Phantom Books and more on the challenges and simple joys of attending school, offering a slice-of-life glimpse into Dalian's adaptation to a normal social environment while still carrying the undercurrent of a hidden secret that must be uncovered.