Ah B (played by Danny Lee) is a plainclothes detective who lives with his mother in a small, old apartment. He is passionate and bold in handling cases, which opened the eyes of his new colleague Ah Jie (played by Eddie). Ah Jie and Ah B have very different personalities, and they only want to pass the exam to be promoted to police officers. Ah B suppressed the two big guys, Xiao Hei and Hong Fan, who lived in Shanshang Village and Shanxia Village respectively, and bought multiple tips through Ah Cheng (played by Tai Bao), a drug addict under Hong Fan. Ah B learned about the criminal information and made contributions, so Ah Jie was also rewarded, and the friendship between the two grew day by day. Soon, Ah Cheng made a big mistake due to repeated drug addiction. He was beaten repeatedly by Xiao Hei and Hong Fan and eventually died. Ah B investigated the cause of Ah Cheng's death and tracked down Xiao Hei, but unexpectedly caused an accident, forcing himself to a dead end, and Xiao Hei had to choose to take risks. The police and the criminals had no choice...