Female police officer Pak Yik-wah poses as a cleaner and works in a fitness centre to gather evidence of the trainer Henry Fung's criminal activities. In the company of sister Yik-mui, the detective attends the centre's anniversary ball where she meets and falls in love with Man Hing-cheong, a well mannered guest with an elegance about him. But Yik-wah is forced to quit when her conservative father Yau-yu finds out about her moonlighting activities. To help the crime leader Wu Hung evade the police, Henry hatches a plan to murder Yau-yu who, like the wanted man, has a mole on his sole. When the sisters come under attack from a mob of gangsters following Yau-yu's disappearance, Man arrives to save the day and reveals his undercover identity. The operative hot on the heels of Wu joins hands with the sisters and lays siege to the gangster's hideout in a heroic effort to rescue the hostage and wipe out the gang.