Interpol captain Lu Yan was once the youngest "criminal-solving legend" in the police force. However, due to a miscarriage of justice in an unsolved case three years ago, the real murderer went unpunished and the victim's family committed suicide in despair. The backlog unit is located in the basement of the police station. It contains twelve unsolved cases spanning ten years, each of which is marked "unsolved."
After the new director took office, he asked the backlog team to restart the investigation within a time limit. When Lu Yan was sorting through the files, he discovered that these twelve cases seemed unrelated - an artist hanged himself in a secret room, a female high school student disappeared on a rainy night, an entrepreneur was killed by a chandelier, and an unknown corpse was found on the railroad tracks... But there were strange similarities hidden in the details: a special bronze bookmark was left at each crime scene, with different Roman numerals (I to XII) engraved on the back of the bookmark, and the deceased held a "foreign object" that had nothing to do with their occupation.
As the investigation deepened, Lu Yan discovered that there seemed to be an invisible hand behind these cases, and the unsolved case that he had misjudged back then was inextricably linked to these twelve cases. The "foreign object" in the deceased's hand pointed to a medical experiment ten years ago. The number on the bronze bookmark corresponded to the experimenter's number, and he himself had already been involved in this revenge chess game that spanned ten years. When the twelfth bookmark appeared, Lu Yan finally understood that these twelve cases were never independent crimes, but a carefully designed "trial", and he was both the pursuer and the subject of the trial.
