Six months ago, Lord Hugh Anthony Disward, also known as Huey, lost his eccentric grandfather, Sir Wesley Disward, a renowned collector of rare books. According to his grandfather's will, Huey must assume guardianship of the Bibliotheca Mystica de Dantalian—an archive containing forbidden knowledge—and care for a mysterious girl named Dalian in order to inherit the manor and all its contents. As Huey settles into the manor, an old rival of his grandfather arranges a meeting with him. Dalian, aware that the rival is Wesley's killer, accompanies Huey and discovers that the murderer possesses a Phantom Book—a cursed tome that Wesley attempted to seal away. When the book endangers them, Huey realizes that the Bibliotheca Mystica de Dantalian and Dalian are one and the same, and she entrusts him with the key to unlocking the knowledge stored within her. Together, Dalian and Huey seal the book away, thus beginning an unlikely partnership as they solve mysteries caused by other Phantom Books.