Tell No One

Zheng Ying, an old police officer who is about to retire, goes undercover as an overseas businessman to trade with Liu Qing's gang. However, he mysteriously disappeared after he successfully caught the gang red handed. Zheng Dong Yu, is Zheng Ying’s daughter. The once arrogant and free spirited girl, grew up over night when her father went missing. In order to find him she became a police woman. Gao Yang, a young police officer that went undercover with Zheng Ying, is also looking for him. He stayed in his undercover role, investigating the disappearance of Zheng Ying. 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 lose, that 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?