Lightning Killer(1967)

Fong Ching-wah (Josephine Siao) assumes the alias of Annie Yuen and works with the police in investigating the homicide of her father Sau-nin, a jeweller. Befriending Lee Yau-sam (Woo Fung), the adoptive son of gangster Lee Tin-fung (Sek Kin), Ching-wah not only wins his trust but also his affection.