James Moriarty, the most fearsome criminal in Victorian London, meets his end after his final confrontation with a famous detective at Reichenbach Falls. Instead of fading into oblivion, he awakens in an unfamiliar world, inhabiting the body of a sixteen-year-old noble girl named Sherry Moriarty. She is a student at Earl Blue Academy, a prestigious school for young ladies, where she was on the verge of taking her own life after enduring relentless and cruel bullying from her fellow noble classmates.

Moriarty retains no memories of his past life, but his extraordinary intellect and his ability to construct perfect criminal schemes remain entirely intact. He witnesses firsthand the insidious abuse Sherry has suffered. In this new world, there is no great detective to oppose him. Seeing the girl's pitiful condition, the criminal mastermind decides to act as a gentleman and form a pact with her. He offers to use his brilliant mind to craft the perfect plans, allowing Sherry to exact a brutal revenge on her tormentors. The bullied young lady effectively dies and is reborn as a villainess without blood or tears, with Moriarty as the ghostly partner guiding her actions from within their shared body.

The central conflict revolves around this dual existence. James Moriarty, the ghost of a criminal genius, and Sherry Moriarty, a tormented noble girl, must cooperate to navigate the treacherous social hierarchy of the academy. The narrative follows their coordinated efforts to systematically dismantle the lives of Sherry's abusers through intricate and untraceable schemes. The series originated from a Japanese novel by Kuromeika that began publication in 2019, and it was later adapted into a webtoon in 2023. The story is also notable for its adaptation into a light anime, a simplified animation format, which premiered in July 2024.