The story continues from "Detective C". The ability of Ah Tan (played by Aaron Kwok) to solve cases has been fully demonstrated, and his friend Feng Ze (played by Liao Qizhi) also feels proud of it, but Feng Ze is still unsuccessful in the police station and is transferred to Officer Lu (played by Patrick Tam), who is famous for his meritocracy. Not long after Feng Ze was transferred, a series of murders occurred in the jurisdiction. The four deaths were unrelated to each other, and the murderer also left quite deliberate clues at the scene. Ah Tan assisted Feng Ze and proposed many possibilities for the murderer under the cold eyes of Officer Lu. Finally, the murderer was initially identified as a schizophrenic patient. During the investigation, the suspect Liang Weiye (played by Cheung Siu Fai) was ill and took hostages. Ah Tan devised a plan to capture him, but unfortunately found that Liang was not the real murderer. Soon, Ah Tan was intimidated by Officer Lu's men, and Feng Ze was hit by someone. The furious Ah Tan found Officer Lu, but was told that the suspect's aggressiveness exceeded his imagination...