Senior inspectors of the task force, Chen Xiaosheng (Ouyang Zhenhua) and Wei Yingzi (Cai Shaofen), who have a stable relationship, finally established a relationship. But Yingzi puts the focus on his career, hoping to strive for the opportunity to be promoted to inspector. However, Xiaosheng has been longing for a family life with children for many years, and the two have constant conflicts. The appearance of the serious case team police officer Kuang Zijian (Lin Wenlong) has put their relationship into crisis. The conflicts and misunderstandings that occurred one after another have caused the two to separate. At this time, Fang Qing (Meng Jiahui), director of the Forensic Department, walked into Xiaosheng's heart. Chen Sanyuan (Teng Liming) is pregnant with Liujia again, and her husband Cheng Feng (Wei Junjie) has also made new breakthroughs in his career and has been promoted to chief inspector. Everything is preparing to welcome this new life. However, the gangster "Hongyingshe" that is expanding its power is becoming more and more rampant, and a police-bandit war is ready to go. "Armed Reaction IV" is the fourth series of Hong Kong TVB's fashion police drama series, directed by Hong Kong TVB's gold medal police drama producer Kwong Yip-sang. From 1998 to 2004, a total of four series were broadcast. In addition to the original cast of Ouyang Zhenhua, Cai Shaofen, Wei Junjie and Tang Limin, this series also has the participation of Lin Wenlong, Mung Yoyo, Cheung Wai-yee and Mai Bao.