The film revolves around the exploits of a detective agency in Hong Kong called Mannix Private Detective Agency. It is headed by the clueless private detective Wong Yeuk Sze with his emotionally drained assistant Puffy. Meanwhile, Lee Kwok Kit, a kung fu expert, who works at a Vitasoy plant factory and spends most of the time doing kung fu tricks to impress a girl, ultimately loses his job. Seeking to find another line of work, Lee attempts to joins Wong's detective agency...