On a rainy night, the fierce Zeus gang leader Jang Dong-su was driving home when he was hit by someone on the road. He was attacked without warning as soon as he got out of the car. He was seriously injured and fought back quickly to barely save his life, but his reputation as a gang leader was severely damaged. The only way to repair his reputation is to find the murderer who attacked him and retaliate fiercely. Jang Dong-su decided to work with detective Zheng Taixi, who believed that the attacker was the serial killer he was tracking. Detective Zheng's boss was dismissive of his reasoning and said that there was no evidence to support his conjecture. Because the killer did not leave any evidence, Detective Zheng had no choice but to use Jang Dong-su's resources to collect information about the serial killer and try to find the killer through similar methods. The two people, each with their own talents and resources, joined forces to start looking for the serial killer codenamed "K". The two people who were chasing the same "prey" also set a rule: whoever finds him first can deal with him at will!