A1's rival, later girlfriend. Michael Tse as "A1" Lam (藍一一; Laam Jatjat), a reporter for the tabloid newspaper "Boom Daily." He consistently finds ways to have Lui Hap hit the headlines. Lui Hap's rival, later boyfriend. Wong Tze-tsuen's cousin. Mandy Wong as Inspector Szeto Kiu (司徒驕; Sitou Giu), known as Madam Kiu, the cold and resolute inspector of West Kowloon's Emergency Unit, and Lui Hap's supervisor. She was a former inspector working in the Airport Security Unit. Wong Tze Tsuen's girlfriend Matthew Ko as Constable Wong Tze-tsuen (王子傳; Wong Zicyun), known as Prince (王子; wongzi), a new young recruit to West Kowloon's Emergency Unit. He is the primary love interest for both Lui Hap and Madam Kiu. Szeto Kiu's boyfriend. A1's cousin. Océane Zhu as Constable Lam Oi-oi (藍愛愛; Laam Oioi), A1's younger half-sister. Born in Hong Kong and raised in Taiwan, Oi becomes a police officer in Hong Kong in order for a chance to meet with A1. Yau Man Chi's love interest, later girlfriend. Wong Tze-tsuen's cousin. Queenie Chu as Constable Mai Ka-po (米家寶; Mai Gaabou), an officer of the Traffic Branch Headquarters (TBH) of the West Kowloon Police Force and one of Lui Hap's best friends. Koni Lui as Constable Lam Long-ning (林朗寧; Lam Longning), known as Long Leg, a police officer of West Kowloon's Emergency Unit and one of Lui Hap's best friends. Grace Wong as Constable Kam Sui-na (金瑞娜; Gam Seoinaa), known as Goldie, an officer of West Kowloon's Emergency Unit and one of Lui Hap's best friends. William Chak as Constable Yau Man-chi (游漫池; Yau Maanci), known as Delay Gor, an officer who has a crush on Oi-oi, later boyfriend. Benz Hui as "Boy Sir" Lui Tsan-nam (呂鎮男; Leoi Zannaam), Lui Hap's father and a retired officer of the VIP Protection Unit (VIPPU) of the Hong Kong Police Force. Pat Ling Lung's husband. Angelina Lo as "Sister Ten" Pat Ling-lung (畢玲瓏; Bat Linglung), Lui Hap's mother and a retired police inspector. Lui Tsan Nam's wife. Ching Hor-wai as Sung Wai-sing (宋慧星; Sung Waising), A1's mother who works as a provider for background actors. Her name is inspired by Shin Hye-sung, a member of the South Korean boy band Shinhwa. Jason Pai Piau as Szeto Wai (司徒威; Sitou Wai), Madam Kiu's father. Candice Chiu as Constable Tong Mei-kei (唐美琪; Tong Meikei), known as Miki, one of Lui Hap's best friends. Ha Ping as Lee Song