The agile and cerebral fighter Kong Yin is invited to join the police SWAT team. Kong is soon sent on an undercover mission to investigate the gang operating at the Happiness Rubber Plant to coerce female workers into prostitution. An indignant Kong joins hands with fellow worker Chow Mei-ha and factory head Wong Chi-kong to expel Blackie Kei whose ruthless and blatant exploitation of the workers has been going unpunished. Facing the loss of a lucrative source of income, Blackie and his underworld bigwig boss Wu Tin-hung intercept the love letters exchanged between Wong and the wife of the general manager Ting Yuk-lan and use the correspondence to extort money from the adulterers. The fearless Chow dons a maid disguise and ingratiates herself with the gangster, followed by a police raid masterminded by Kong to crack down on the notorious gang.

He Shaoping is a studious factory worker who falls in love with her teacher at her evening classes.