The series takes place a year after the 2nd installment.
Chan Siu Sang is single and all alone, his old love Chu So Ngo married the doctor that treated her son and left the police force. Then he meets Wai Ying Zi, a rookie police officer that is under Chan Sam Yuen Police Traffic Department unit. The two get off on the wrong foot due to misunderstandings. Wai Ying Zi who is eager to show off her skills seems to get into a lot of trouble. She is deemed reckless and rash. Later on, Ying Zi joins Siu Sang's CID unit which leads to the two bickering non-stop. After Siu Sang saves Ying Zi life on one of their investigations she learns to respect him and the two become friends. Chan Sam Yuen is promoted to the head of the Police Traffic Department. She and Ching Fung are also now parents to a pair of girl/boy twins, but their marriage is not as happy as it seems as the two continue to have quarrels in their marriage. With marital problems at home, Sam Yuen becomes a cold, unreasonable and mean boss at work. When a case similar to the psychotic serial rapist in the last series arises Sam Yuen starts feeling threaten and insecure even though the culprit Bao Gwok Ping is still locked up in jail. It seems Bao Gwok Ping has been communicating with someone on the outside who agreed to take on his split personality persona and continuing his crime spree. Due to Sam Yuen's carelessness her son is kidnapped and killed by the new culprit. This causes Sam Yuen and Ching Fung marriage to be in further jeopardy when he blames her for the death of their son.
The protagonist, Yang Guo, is the orphaned son of Yang Kang, the antagonist in The Legend of the Condor Heroes. The couple Guo Jing and Huang Rong raises Yang Guo briefly before he is sent to the Quanzhen Sect for better guidance in moral values and orthodox martial arts. In Quanzhen, Yang Guo is often picked on and bullied by his fellow students, and even his master, Zhao Zhijing, is biased against him. Yang Guo flees and ventures unknowingly into the nearby Tomb of the Living Dead, where the Ancient Tomb Sect is housed. He is saved by Xiaolongnü, a mysterious maiden of unknown origin, and becomes her apprentice. They live together in the tomb for many years until Yang Guo grows up. After being attacked by Li Mochou, they leave the tomb and stay on the mountain. Xiaolongnü develops romantic feelings for Yang Guo and after a while, he falls in love with her.
However, their romance is forbidden by doctrines of the Confucianism society of that time. Throughout the story, their love meets with several tests, such as the misunderstandings that threaten to tear them apart and the encounter with Gongsun Zhi. Finally, after their reunion and marriage, Xiaolongnü leaves Yang Guo again, owing to her belief she cannot recover from a fatal poison, and promises to meet him again 16 years later. While Yang Guo is wandering the jianghu alone, he meets several formidable martial artists and a giant condor. His adventures gradually mould him into a courageous martial artist, whose prowess matches the Greats of his age. Yang Guo serves his nation by helping the Han Chinese citizens of the Song Dynasty defeat the Mongol invaders. At the end of the novel, he is reunited with Xiaolongnü and they are recognized as heroes of their time.
