The fourth film of the 5-film series The Best Secret Agent series of taiyupian (Taiwanese-language cinema), which was also dubbed into a Mandarin version.

Tenn Kong-Hui is a private eye. Kong-Hui’s ex-lover, Tai-Giok is a personal assistant to a steel company’s chairman. By spying on Tai-Giok, KongHui discovers many dirty secrets of the people who work at the steel company and decides to blackmail each one of them. When Kong-Hui is found dead in his apartment one day, the police detective has identified five suspects. However, as the detective digs further into their stories, he finds that all of them have alibis. Just when the investigation seems to hit a dead end, a sixth suspect suddenly emerges…