Chan family •
Bobby Au-Yeung 歐陽震華 as Chan Siu-Sang 陳小生 - IP. His CID career ended when a criminal shot him in the foot. His parents died when he was young, he was raised by his sister-in-law Wong Yee Mui. He is now working as a Firearms Officer with the CID. •
Mimi Chu 朱咪咪 as Wong Yee Mui 王二妹 - Chan Siu-Sang's sister-in-law and Chan Sam Yuen, Sei Hei, Ng Fuk's mother. When her husband died she raised his younger brother and her three daughters alone. •
Joyce Tang 滕麗名 as Chan Sam Yuen 陳三元 - Chan Siu-Sang's niece and Wong Yee Mui's eldest daughter. An ambitious rookie female cop who puts her life at risk because of her devotion to her job. Patrols for the Yau Ma Tei Police Station's Sub-Patrol Unit then transfers to Ching Fung's RCU Team 1 along with Chu So Ngor. • Koey Leung 梁雪湄 as Chan Sei Hei 陳四喜 - Chan Siu-Sang's niece and Wong Yee Mui's middle daughter. • Sherming Yiu 姚樂怡 as Chan Ng Fuk 陳五福 - Chan Siu-Sang's niece and Wong Yee Mui's youngest daughter.
Yue family (After Yue Wing Choi's divorce with Chu So Ngor, it is now the Chu family) •
Esther Kwan 關詠荷 as Chu So Ngor 朱素娥 - A desk duty police officer who lived a carefree life until her life is turned upside down in a short period of time when she is transferred to the patrol unit and her husband leaves her for another woman. •
Emotion Cheung 張錦程 as Yue Wing Choi 余永財 - Chu So Ngo husband then ex-husband. He leaves his wife and son for his pregnant mainland mistress. • Ting Lik 丁力 as Yue Ka Lok 余家樂 - Chu So Ngor and Yue Wing Choi's 10-year-old son. He forms a close friendship with Chan Siu-Sang when his father leaves the family.
Ching family •
Marco Ngai 魏駿傑 as Ching Fung 程峰 - IP of RCU Team 1. Chan Sam Yuen's superior and later boyfriend. •
Chor Yuen 楚原 as Ching Sau Chung 程守忠 - Ching Fung's father. • Helen Ma 馬海倫 as Ho Kam Mui 何金梅 - Ching Fung's mother.
West Kowloon CID • Kwok Tak Shun 郭德信 as Kwok Sir 郭Sir • Leung Kin Ping 梁健平 as Peter • Lee Chi Kei 李子奇 as Superintendent Ho 何Sir •
Joe Ma 馬德鐘 as Leung Heung Dong 梁向東 • Timothy Siu 邵傳勇 as Au Chi Keung 歐志強 •
Li Shing-cheong 李成昌 as Sergeant Pao Ting Tin 鮑頂天 • Ben Wong Tin-Dok 黃天鐸 as Superintendent Wong 黃Sir • Chan Dik Hak 陳狄克 as Station Sergeant (Briefing officer in episode 1) 時沙 • Mok Ka Yiu 莫家堯 as Kwan Sir 關Sir
Criminals and suspects • Ching Siu Lung 程小龍 as Cheng Chung Yee 鄭忠義 • Willie Wai Kar Hung 韋家雄 as Cheng Chung Seon 鄭忠信 • Akina Hong Wah 康華 as Wong Wai Sum 王慰心 • Johnson Law 羅莽 as Cheung Pau 張炮 • Koo Ming Wah 古明華 as Cheung Ming Wah 張明華 •
Angela Tong 湯盈盈 as Siu Ding 小丁 • Candy Chiu 趙靜儀 as Ma Siu Ling 馬小玲 • Ricky Wong Chun Tong 王俊棠 as Nip Sai Guen 聶世官 • Josephine Lam 林其欣 as Yuen Siu Bik 袁小碧 ==Criticism==