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.
When Hong Kong is rocked by multiple gruesome murders, the police forms a task force to investigate. Jun, once a brilliant detective who suffered a mental breakdown, begins his own investigation. Eventually, the police learn that the murder victims are all suspects of cold cases being rubbed out by a figure known as "The Sleuth". Now, Jun and a detective from the task force are on a race against time to beat the brutal killer at its own game.
After suffering life changing injuries in the line of duty, bomb disposal officer Fung turns his back on the police. But when a devastating series of bombings sweep Hong Kong, the police suspect their former ally may be involved after he is found unconscious at a crime scene. Now faced with memory loss and recalling only fragments of his former life, Fung sets out to uncover the truth and find out who he really is.