The big chase (1966)

Tse Mei-chen is deeply concerned about her only family, sister Bo-chen who is obsessed with perfecting her detective sensibilities. One day, Bo-chen returns home in panic to relay to her sister and her boyfriend detective Ma Tin-lung the horrifying murder of Siu-ying by her husband Tsui Kai. But a subsequent visit to the couple's, the cousin of Bo-chen's best friend Wong Kam-fung, proves the alleged crime false. Incognizant to all, the victim was Siu-ying's twin sister Kwok-ying, who bore witness to Tsui's misappropriation of their wealth for drug trafficking. Refusing to abandon the probe, Bo-chen is held up by Tsui. Deeply perturbed by Ma's investigation into his secret dealings, Tsui coerces Mei-chen to distract her boyfriend long enough for his escape. Refusing to bow to the threat, Mei-chen informs Ma who leads his squad to the rescue of the sister and arrests Tsui and his accomplices.