Terry Yue Siu-bo, a single father who single-handedly raises his two children, Natalie and Nicky, to young adulthood after his wife's death. Nicky works as a dolphin trainer at Ocean Park and Natalie goes to school with Ella, Nicky's girlfriend. Natalie's boyfriend, Jason, is a musician who does not speak Cantonese very well, and in his first scene, gives Natalie a pet pig. Siu-bo works as a Chinese traditional bonesetter and has kung fu skills, which he has passed on to his children, who display prowess while fighting each other in sibling disputes. Siu-bo tells exaggerated stories to his children and their friends, but they think they don't believe them to be true thus causing a lot of embarrassment to Nicky and Natalie. Rocco, an ex-CIA Agent out for revenge, kidnaps Siu-bo and demands information about a former spy whom Siu-bo knew. Siu-bo refuses to tell him, and Rocco threatens to harm his children if he does not give in. During this time, Uncle Chiu discovers Siu-bo's shop trashed and calls up Nicky to tell him of his father's disappearance. Finding a secret room at the back of his shop, Nicky finds out of his great past as a G4 agent assigned to protect former spies. Seeking more information, Siu-bo is injected with a truth serum by Rocco's men, and in his degraded mental state he reveals that he hid memory cards of his past activity in the lucky charms of his children. Rocco sends agents to Natalie, who is acting in a play, but Nicky manages to get to her and escape with some help from Ella and Jason. As they hide out in Jason's house, Natalie finds out about the memory card in her charm and has Jason try to open it. They then find out that the card needs the other memory card to function, but Nicky in his haste to get to the shop left it in his locker at the park. Nicky and Natalie then attempt to get it during the dead of night, but are intercepted by two of Rocco's minions. After defeating the minions, a phone rings, and they get into direct contact with Rocco, who threatens their father's death if they do not help him in his quest for revenge. He gives them one day to find the agent, and then cuts the conversation. Nicky and Natalie get back to Jason's house and find out that they require voice authentication from their father to access the file. Jason works through the night to create a file that would match Siu-bo's voice. During this time Siu-bo attempts to escape, but is foiled by Rocco's son, who is extremely adept with a bo staff. Jason finishes the file, and is finally able to access the database. They find out that Rocco's target is actually Uncle Chiu, who turns out to be the same agent that left Rocco paralyzed and captured him. Nicky and Natalie try to leave to recover their father and find Uncle Chiu, but Jason traps them in his studio, and reveals that he is Siu-bo's co-agent and does not want them to get hurt. He also reveals that his romantic intentions with Natalie are real, and not just a cover story. Jason makes his way to Uncle Chiu to warn him to escape, and the old Uncle initially accepts, asking for a final moment to spend with his granddaughter. An ambulance creates a distraction from Jason to reveal Uncle Chiu attempting to escape by climbing and running across rooftops. The siblings, initially thinking they were left trapped in Jason's home, find an air vent to escape in, and follow Jason to Uncle Chiu's restaurant. Jason chases Uncle Chiu, but injures his ankle on attempting to jump between buildings and is saved by a fire hose thrown out by Uncle Chiu. Nicky and Natalie catch up to him, and ask him for help in saving their father. He relents, and Jason calls Nicky to throw him his car's keys, so they could get Uncle Chiu to Rocco in time. Nicky and Natalie take a boat to Rocco's lair, and demand to see their father. Rocco reveals him to be trapped in a tank rapidly emptying of air, and rebuffs them without the agent he is looking for. Uncle Chiu shows up, and Rocco calls in his men to kill them. They fight their way through everyone, with Natalie breaking out Siu-bo by applying a kung fu technique he taught her in her youth, Nicky saving Uncle Chiu from a killing blow and defeating Rocco's son. Nicky leaves Rocco unharmed after he makes him fall off his wheelchair, and everyone manages to leave Rocco's lair alive. In the ending scene, Jason comes to Siu-bo's home to apologize to Natalie, which she accepts. Nicky finally gets the courage to have a French kiss with Ella, and Siu-bo and Uncle Chiu play a game of chess, with Chiu's granddaughter watching.
