In order to cut off the drug trafficking network in South Korea, the police chief Min Hongji (Son Changmin) set up a special search department. In order to avenge his brother, prosecutor Ji Hengmin (Lee Jae-yoon) served as the team leader of the special search department, specializing in catching drug lords. Zheng Shixian (Jung Kyung-ho), nicknamed "Son of the Doctor", was born in a poor family. When he grew up, he mixed into the Seoul Drug Trafficking Center with his outstanding talent. Li Jingmei (Go Na-eun) was Zheng Shixian's childhood playmate. Now she has entered the police force and is in love with Ji Hengmin. Zheng Shixian learned that a drug deal would be held at the hotel of Li Zhenshu (Kim Yu-mi), who had done him a favor. He rushed to the hotel but found that it was a trap set by others. He was stabbed while escaping. He went to the convenience store to find medicine and met a robber. Zheng Shixian knocked the robber unconscious with his injuries. Jingmei's sister Minxiu (Nam Gyu-ri), who worked at the convenience store, helped him deal with the wound. In the gunfight with Xiyan, Jingmei pointed her gun at Shixian. When their eyes met, Jingmei found that the other person was actually her childhood playmate Shixian's brother...