Lin Yuan is a twenty-year-old orphan working as a food delivery rider in the city of Haishi, where his primary goal is to save enough money to purchase a home. After saving two children from an oncoming truck, he suffers a concussion and is hospitalized. While recovering, a voice in his mind activates the Criminal System, binding him to a digital library containing detailed accounts of criminal cases. The system grants him the ability to read and retain all information instantly through the skill Read Once, Never Forget, and forces him to study the cases to unlock further enhancements, including increased physical strength.
Upon discharge, Lin Yuan returns to his delivery job but is quickly drawn into a murder investigation at a local restaurant. He provides crucial testimony to the police regarding the missing wife of the victim, Liu Ming. His observations lead the police to discover that Liu Ming was murdered by two people, not one, and that the case is connected to a larger drug trafficking operation. Acting on information from a colleague, Lin Yuan tracks down the perpetrators attempting to destroy evidence at a sealed property. He confronts three armed men, incapacitates them using techniques learned from the Criminal System, and calls the police, leading to the arrest of the drug dealers.
The investigation reveals a connection to a series of unsolved murders of teenage boys from a year prior. Lin Yuan recognizes the modus operandi from the Criminal System cases and realizes another user may exist. He approaches the District C Police Station and offers his services to solve the cold case. Using his photographic memory and deductive skills, he identifies a suspect, Zhong Anguo, by analyzing surveillance footage and crime scene details that the police had overlooked. He directs the police to dig near Twin Bridges, where they recover a raincoat with blood evidence, leading to Zhong Anguo's arrest.
During the interrogation, Lin Yuan determines that Zhong Anguo is a scapegoat protecting his son, Zhong Wei, who is being manipulated by an unknown mastermind. Lin Yuan pressures Zhong Anguo by threatening to freeze his son's assets, successfully breaking the suspect's silence. The police station, impressed by his results, offers Lin Yuan a temporary consultant position for one week to solve remaining cold cases. Lin Yuan accepts the role, moving into the police archives where he begins reviewing old files alongside a young female officer, Zheng Yunyin. His work attracts the attention of visiting consultants from other districts, who underestimate him due to his youth and lack of official credentials. Lin Yuan proceeds to analyze a locked-room murder case, demonstrating insights that challenge the experienced investigators and hinting at a deeper involvement in the criminal underworld that the system has revealed to him.
