The Secret Code (1965)

Leader of the Celestial Devil Gang Mo Fu ends an underling to infiltrate the house of code expert Cheung Yuet-ting in pursuit of the Mafia's secret intelligence. The unyielding man is killed, and the Mafia is framed for the crime. Cheung's instrumental role in the Mafia is succeeded by his daughter Oi-lan, who leads both gangs onto a deadly chase. Just then, Oi-lan's bosom friend Chan Yu-lam emerges from years of oblivion as a Mafia member and offers the wanted woman protection and assistance in retrieving the late father's cache. Mo's underling Lau Kei-fung is assigned the task of playing the confidence game in the Cheung household, preempting Oi-lan from accessing the classified information and abducting both Oi-lan and Chan before the Mafia can reach the key witness. Acting on a tip-off, the police raid the apartment and arrest both gangs. Chan, the undercover police officer, gains both Oi-lan's trust and affection. (Synopsis based on audiovisual materials)