Cheung Sai-Lun (Vincent Wong): a struggling actor from Ohio with Hong Kong heritage comes back to Hong Kong to audition for a role in a film. However, he is wrapped up in a murder case involving the murder of triad boss: Old Chiang and his 2 sons, he is asked by Rachel Koo (Crystal Fung): a senior inspector of OCTB to become a spy in a triad for the police alongside the pre-existing spy: Ko Ban (Owen Cheung). He is cast as the Chiangs' long lost third son with the fact that the real son had been killed in a gang war beforehand....
