Banker Fung Yan-tsang is a seasoned criminal in fraudulent activities. The righteous cat burglar Ham Siu-fo has issued a deadline for Fung to return the scammed money. Despite the obstacles put up by Fung's allies Chow Wai-pak and his stepwife Julie, Ham still manages to reclaim the money which is accordingly returned to the customers. In the process, Ham is reunited with her long-lost twin sister Katherine, Chow's daughter. Since losing her mother whose health took a turn for the worse after Chow's marriage to Julie, Ham has undertaken a chivalrous course in the footsteps of her aunt. She thwarts the scam marriage set up by Fung for Katherine and his idle son, using the servant Chu Yat-keung as bait, and exposes Fung's illicit affair with Julie. Crossing boundaries of class and wealth, the servant Chu and Katherine become man and wife. A happy Ham leaves, continuing to devote her life to the causes of social justice.

Lau Leung-wah plays the titled character, a Chinese Robin Hood who robs the rich to help the poor. She is an early Republican Era Mulan, who switches effortlessly between charming gentility and agile ferocity, and Lau personifies her character's duality with a balance of grace and vigour. Chang Cheh, on the verge of fostering seismic changes in cinema with his martial-arts machismo, pens a script that captures the spirit of changing Chinese womanhood, underscored by a conflict between Black Butterfly and her father, a veteran detective.