"Zheng Ying, an old police officer about to retire, goes undercover as an overseas businessman to trade with Liu Qing's gang. However, he mysteriously disappears after he successfully catches the gang red-handed. Zheng Dong Yu is Zheng Ying’s daughter. The once arrogant and free-spirited girl grew up overnight when her father went missing. In order to find him, she became a police officer. Gao Yang, a young police officer who went undercover with Zheng Ying, is also looking for him. He stayed in his undercover role, investigating Zheng Ying's disappearance. Six years later, Lei Nai Wu, the key figure of Liu Qing's gang and the last person to meet Zheng Ying, was released from prison. At the same time, a mysterious killer is on the loose, who is trying to kill Lei Nai Wu. At the time, Gao Yang ventured to save Lei Nai Wu. Lei Nai Wu told him that this killer was the real murderer of Zheng Ying. 
What has truly happened to Zheng Ying?"