Sniper Lee Ho-yeung (Michael Tse) left the Special Duties Unit as he failed in an operation, and since then he has gradually developed personal enmity towards his co-worker and good friend Ko Chun Kin (Eddie Cheung).
Ho-yeung becomes a yacht merchant and then becomes a president of a Firearms Association, colluding with organised crime syndicates on the sly. Taking advantage of the trust laid upon him by a detective of the Organised Crime and Triad Bureau, Sheung-koon Ming-chu (Kate Tsui), he has quite a grasp on police operations that raid on the crime syndicates. On top of that, with his girlfriend Lai Chan (Eliza Sam) being a member of the Special Duties Unit, Ho-yeung gains first-move advantage in all respects. On the flip side, Chun-kin has been kept in the dark for the whole time, until he finds there is something suspicious regarding the criminal’s modus operandi in several murder cases. Later on, owing to a money laundering case, Ho-yeung deliberately approaches Chun-kin’s good friend, Wong Yeuk-ling (Kathy Chow), who learns that Chun-kin was the sniper who shot her in the head many years ago. Without anyone noticing, a tense standoff between the brothers is about to unfold.
Vincent Lam as Kong Chi-ngai (江志毅), Senior Inspector of the SDU, and also Ko Chun-kin's superior officer and good friend.
Eddie Cheung as Ko Chun-kin (高晉堅), nicknamed GoGo Sir, Station sergeant and sniper instructor of the SDU. During an operation in the past, he accidentally shot hostage Wong Yeuk-ling in the head. Chun-kin does his best to make it up to her and they later develop a romantic relationship. He is good friends with Lee Ho-yeung, who is like a brother to him and along with Ho-yeung, he is Sheung-koon Tin's apprentice, who is also a fatherly figure to Chun-kin.
Eliza Sam as Lai Chan (黎珍), the only female member of the SDU who strives to become Hong Kong's first female sniper. She meets Lee Ho-yeung, whom she secretly admires, at the Firearms Association, and when Ho-yeung sees potential in Chan, he takes Chan as his disciple and teachers his sniping skills to her.
William Chak as Lau Kwai (劉貴), nicknamed Tiger, a member of the SDU sniper team who idolizes Lee Ho-yeung.
Steven Cheung as On Ah-chit (安亞哲), nicknamed Energy, a member of the SDU sniper team who develops a crush on Lai Chan.
Otto Chan as Cheung Ching-yee (蔣正義), a member of the SDU assault team.
Yeung Chiu-hoi as Pao Chi-chung (包子忠), a member of the SDU assault team.
Alan Wan as Cheung Pei-yan (張彼仁), a member of the SDU assault team.
Nathan Ngai as Lam Pak-wing (林伯榮), a member of the SDU assault team.
Raymond Tsang as Yau Yiu-wai (邱耀威), a member of the SDU assault team.
Lau Tin-lung as Chiu Yung (趙勇), a member of the SDU assault team.
Henry Lo as Koon Man-fu (管萬夫), Superintendent of the Organised Crime and Triad Bureau who initially doubted Ming-chu's abilities.
Joseph Yeung as Tang Wai-leung (鄧偉樑), Chief Inspector of OCTB.
Kate Tsui as Sheung-koon Ming-chu (上官明珠), Senior Inspector of OCTB who is well respected by her subordinates due to her work abilities and kind nature. She is the daughter of Sheung-koon Tin and grew up with his father's apprentices, Chun-kin and Ho-yeung, whom she views as her older brothers. Ever since as an adolescent, Ming-chu has had a crush on Chun-kin.
Chan Wing-chun as Wat Chin-kei (屈展基), Ming-chu's subordinate.
Rocky Cheng as Mo heung-tung (毛向南), Ming-chu's subordinate.
Russell Cheung as Kwok Wai-lun (郭泰倫), Ming-chu's subordinate.
Apple Chan as Pang Kei (彭棋), Ming-chu's subordinate who went undercover in Kei Tim Corporation where her identity was exposed and severely beaten as a result.
Kathy Chow as Wong Yeuk-ling (王若玲), ex-girlfriend of Albert Yip, an accountant who was involved in a money laundering case. Yeuk-ling was held hostage by kidnappers after Yip and during the incident, Chun-kin accidentally shot Yeuk-ling in the head. Chun-kin does his best to make up to her by providing her a job at his brother's insurance company, and later investing in to a cafe with the help of Ho-yeung. Not knowing that Chun-kin was doing all this to make it up to her, she develops a relationship with him. Later, thugs that were after Yip came back after her and during an incident where her younger brother Chi-hong was shot by a hitman, she goes through a personality change and seeks help from Ho-yeung to teach her how to use guns to seek revenge.
Miki Yeung as Wong Yeuk-sam (王若心), Yeuk-ling's younger sister. She was once kidnapped along with her sister by a casino owner in an attempt to blackmail Lee Ho-yeung. Eventually, she and her sister were rescued by Ho-yeung
Leo Lee as Wong Chi-hong (王子康), Yeuk-ling and Yeuk-sam's younger brother who recently returned to Hong Kong from studying abroad. He was later shot and seriously injured by a hitman who was after Yeuk-ling.
Suet Nei as Law Oi-yau (羅愛友), Ko Chun-sek and Ko Chun-kin's mother.
Jimmy Au as Ko Chun-sek (高晉碩), Chun-kin's older brother who is an insurance manager and the main financial support of the family. He is married to Kwok Mei-kam and has a child, Ko Fai-ting.
Kayi Cheung as Kwok Mei-kam (郭美金), Chun-sek's wife and Fai-ting's mother
Chun Wong as Ting Sheung-sin (丁上善), the president of Kei Tim Corporation and Lee Ho-yeung's employer. Sheung-yin plans to pass down his business to his son, Fung, instead of her daughter, Hau, who is much more competent. He later schemes with his son to expose his daughter's crime evidence to the police and Ho-yeung kidnaps him and his son.
Alice Chan as Ting Hau (丁巧), the vice president of Kei Tim Corporation and gives her best to the company despite her father's favoritism of her younger brother instead. She colludes with her loyal right-hand man, Ho-yeung, for whom she has feelings.
Jack Hui as Ting Fung (丁峰), Sheung-sin's son and Hau's younger brother who is rather useless and not serious. He later schemes with his father to expose his sister's crime evidence to the police and Ho-yeung kidnaps them.
Michael Tse as Lee Ho-yeung (李浩陽), a former member of the SDU sniper team who was dismissed after he killed a suspect during an operation. He is good friends with Ko Chun-kin, who regards Ho-yeung as a superior marksman. Ho-yeung, who has an emulative personality, feels bitter towards Chun-kin when he testified neutral to their superior officers, indirectly causing Ho-yeung's dismissal from the police force. On the surface, Ho-yeung works as a yacht merchant and trainer at the Firearms Association, but in actuality, he works as a hitman for Ting Sheung-sin and Ting Hau, killing people he believes that cannot be punished by law. Ho-yeung engages in a battle of wits with Chun-kin when the latter suspects his involvement of recent murder cases.
Ma Koon-tung as Cha Siu-po (查小寶), Ho-yeung's personal assistant who is an expert computer hacker.
Joe Junior as Choi Man-sing (蔡萬承), supervisor of the Firearms Association.
Andes Yue as Albert Yip (葉以博), Yeuk-ling's deceased boyfriend who was an accountant and was involved in a money laundering case.
Eric Chung as KC Lau (劉國忠), a property developer who scammed Ting Fung, causing Kei Tim Corporation to lose money. He was later abducted by Ting Hau and Chan Mo-chi with the help of Ho-yeung.
Parkman Wong as Hung Kwok-choi (洪國才), head of an illegal bookmarking organisation and a triad leader who was entrusted to launder US$50 million, but the funds went missing.
Stephen Ho as Eagle Eye (鷹眼), a hitman working under Hung Kwok-choi whose marksman skills proves to be a match to Lee Ho-yeung. He once shot and seriously injured Chi-hong while trying to kill Yeuk-ling.