A group of friends who grew up together were separated after a building that collapsed changed their fates forever. When they meet again many years later, their identities have become very different that it is difficult to distinguish between friend or foe, yet they continue to struggle between justice and friendship.

Set in Hong Kong, China, four years after the events in Line Walker, Sit Ka-keung (Raymond Lam) continues to work as a Hong Kong Police Criminal Intelligence Bureau (CIB) undercover officer, while Cheuk Hoi (Michael Miu) opens a coffee shop after being released from prison. CIB Chief Inspector Cheung Kei-gee (Mandy Wong) suspects Check Hoi of joining the triad and investigates him. The Security Bureau establishes Security Intelligence Agency (SIA), a new intelligence department. The principal investigator of SIA, Wai Chok-wing (Kenneth Ma) invites Tsui Tin-tong (Benjamin Yuen) to join SIA. Chum Foon-hei (Benz Hui), who was thought to be killed by Bao Seed, returns to Hong Kong to track down the leader of an international crime organization, Eternity. The true identity of Wai Choi-wing is later revealed to be Ngai Tak-lai, the younger paternal half-brother of Victor Ngai Tak-shun...

Thirty years ago, hardened criminal Yip Siu-tin is arrested for armed robbery and sentenced to prison. Siu-tin’s daughter, who has handled the loot, changes her name to Cheung Sum-yuet and starts a new life. She also gets married to yacht company boss Yen Ho-yin. Meanwhile, Chong Chi-kiu is a kid left behind by an accomplice who has died because of the robbery. Kind-hearted Tang Sing-him becomes his foster parent. A traffic accident causes Chi-kiu and Sum-yuet to run into each other again. But this accident somehow has something to do with Siu-tin, who is just released from prison. Sum-yuet can no longer avoid Siu-tin, who is a nightmare to her. Her marriage also has certain issues. Police officer Yeung Yan-hiu intervenes by launching an investigation, and she keeps going after Siu-tin and Chi-kiu. Unresolved grudges for thirty years are again put on the front burner. Everyone implicated in a robbery of yesteryear is drawn into this mess.