In Mong Kok, 1993, at a no-parking zone, Mang Biao, a small-time gangster, refuses to move his car despite being ticketed, even with his boss’s backing. Yang Guangyao arrives on the scene, and after understanding the situation, tries to cooperate with the police by asking Mang Biao to hand over his car keys. Unexpectedly, Mang Biao’s boss appears and deliberately drops the keys into the sewer in front of the police, attempting to leave. Yang Guangyao immediately chases after him, intending to search him, suspecting his odd behavior indicates drug use. Without waiting for a response, he decides to investigate the man’s shop and has the other car locked up. The man has no choice but to compromise.
After dealing with the parking incident, Yang Guangyao moves on to another case, a homicide. He quickly arrives at the crime scene and greets the newcomer, Liu Weitao. They inquire about the details of the case and learn that no murder weapon was found at the scene. Upon learning the deceased’s name is Deng Rongtian, Yang Guangyao begins to examine the cause of death. The newcomer, overwhelmed by the blood, feels the urge to vomit. Yang Guangyao stops him and helps him calm down. Soon, the police bring in some suspects for questioning, but they refuse to cooperate and deliberately cause trouble. After dealing with the troublemakers, Yang Guangyao reports the situation to his superior, believing it doesn’t look like an indoor robbery. Before leaving, his superior reminds him not to be impulsive.
Unexpectedly, a series of murders occur. Yang Guangyao, as a police officer, rushes to each crime scene to observe the surroundings, but finds no clues. Even a social worker near a school becomes a victim. The police classify these cases as homicides. When they arrive at the scenes, they find the victims’ deaths resemble that of “Black Ghost Tim.”
At night, Yang Guangyao sits by the street, drinking beer heavily. He then jumps into the river for a swim. After coming ashore, he analyzes the case and goes straight to the morgue to examine the bodies. He discovers a needle mark on one of the victims and decides to re-examine the other three.
The next day, after sending his wife and daughter off, he continues to investigate the case. After a phone call, he follows a lead and finds Mai Zhihong, who was once admitted to a mental hospital. He is shocked after hearing Mai’s words and decides to investigate the person who left him the message. He continues to observe Mai in the interrogation room. While following a lead, another murder occurs, this time a firefighter. Yang Guangyao rushes to the crime scene. Upon returning, he immediately finds Mai Zhihong and talks about the murders, but Mai remains unmoved and utters some strange words. Soon, Mai deliberately injures himself with a stick and calls for help from the police. Yang Guangyao is framed by him. His superiors suspend him from duty. Yang Guangyao, feeling wronged, believes Mai Zhihong is the murderer.
After being suspended, he visits his family. Unexpectedly, his wife and daughter are almost killed in an explosion meant for him.
On a rainy night, Yang Guangyao encounters an unidentified person in an underpass. He chases the person relentlessly, ignoring the heavy rain. He pursues the person into an elevator but is knocked unconscious. When he wakes up, the person has already escaped. He looks around and wanders the streets.
