Lynn and her sister Sue are computer hackers, assassins and espionage specialists who use their late father’s secret satellite technology to gain an advantage over their rivals and law enforcement agents. At the beginning of the film, they infiltrate a high security building and assassinate Chow Lui, the chairman of a top company in Hong Kong.
After their successful mission, a police inspector named Kong Yat-hung is assigned to investigate the case and she manages to track down the assassins. In the meantime, Chow Lui’s younger brother Chow Nung, who hired Lynn and Sue to kill his brother so that he can become the chairman, wants to kill the assassins to silence them. The cat-and-mouse chase becomes more complicated as both the police and the thugs are out to get Lynn and Sue.
Sue has always been playing the role of the assistant by staying on the computer and helping to disable the security systems and giving instructions on navigating the area, while Lynn, who is older and more experienced, does all the field work. Sue is jealous and thinks that Lynn refuses to let her participate more actively because she is less adept, but actually Lynn is trying to protect her sister from danger. Their relationship becomes strained when Lynn falls in love with her friend’s cousin Yen and wants to give up her job and marry Yen. Sue intends to continue her career as a contract killer so that she can prove that she is as good as her sister.
Kong Yat-hung tracks down Sue in a bakery, where Sue is buying a birthday cake, and this leads to a frantic car chase. When Sue realises that she is being cornered by the police, she calls Lynn at home and asks her sister for help. At the same time, Chow Nung’s assassins break into the house and kill Lynn and frame Kong Yat-hung for the murder. Sue escapes from the police and finds out the true identities of her sister’s killers from the CCTVs in the house. She goes to see Kong Yat-hung and offers to help her clear her name, but Kong must assist her in avenging her sister. Left with no choice, Kong Yat-hung agrees to team up with Sue to hunt down and kill Chow Nung and his henchmen.