In the near future, a time when cyberization has become commonplace, the protagonist Hayate Kisaragi, a graduate of the prestigious educational institution [Academy] known for producing exceptional talent, runs a detective agency in his hometown, despite graduating at the top of his class and having no interest in status or fame. Seraphina Graciani, a current student of the Academy, ends up working with him under the pretext of training, somewhat forcibly. Together, they have solved small cases such as finding lost pets and investigating infidelities. One day, Hayate receives a strange request from his former classmate Adele Forgan. The request arises after her grandfather, the head of the Forgan family, falls gravely ill, and her relatives begin dying under suspicious circumstances one after another. Each of the deceased reportedly mentioned seeing "a woman in a red dress" just a few days before their deaths. "You have to protect us. Us three sisters. And I want you to uncover the truth behind the curse—the Crimson Lady." Curiosity piqued by Seraphina’s relentless urging and unable to refuse a request from an old friend, Hayate accepts the case. The two are invited to the Forgan family mansion, where they begin tracing the shadow of the Crimson Lady. "Well, I guess when a real big case actually shows up, you think... this isn’t detective work at all." "Yeah…"