Forensic Heroes IV

Senior Forensic Chemist Ko On (Raymond Wong) from the Forensic Science Division, Senior Forensic Pathologist Man Ka-hei (Selena Lee) from the Forensic Pathology Division, and Senior Inspector Kwok Fai-wong (Shaun Tam) from the Kowloon West Regional Crime Unit, formed a crime-solving triangle with their professional teams. The childhood regrets of hot-blooded reporter Chris Tsui (Roxanne Tong) who were closely related to Ko On sister abduction years ago. Scientific Evidence Officer Shui Wai-ming (Alice Chan) became a murder suspect upon her boyfriend's murder while Sergeant Ko Ching (Rebecca Zhu) who is a Sergeant who persistently investigating the truth of her sister's abduction alongside Ko On (Raymond Wong). The crime-solving triangle firmly believes that good always triumph over evil and fights for justice.

A costume fitting press conference was held on 24 October 2018. Principal photography began in October 2018 and concluded in March 2019, with some scenes filmed in Taiwan. The blessing ceremony was held on 21 January 2019.^[1]

In April 2019, Jacqueline Wong, who was cast as Chris Tsui, was found to be involved in a cheating scandal. Producer Mui Siu-ching confirmed that the role would be recast and all scene with Wong would be reshot.^[2][3] Roxanne Tong took the role^[4] and reshoots lasted from June 2019 to July 2019.

• Raymond Wong as Dr. Ko On (高安), a senior chemist and laboratory supervisor from the Forensic Science Division.
• Selena Lee as Dr. Man Ka-hei (聞家希), a senior forensic pathologist from the Forensic Pathology Division.
• Shaun Tam as Kwok Fai-wong (郭輝煌), a senior inspector from the Kowloon West Regional Crime Unit.
• Alice Chan as Queen Shui Wai-ming (水慧明), a scientific evidence officer (SEO) from the Forensic Science Division.
• Rebecca Zhu as Ko Ching (高靖), a sergeant from the Kowloon West Regional Crime Unit.
• Roxanne Tong as Chris Tsui (徐意), an online news reporter.

• Fred Cheng as Charm Ting (湛霆), a scientific evidence officer (SEO) from the Forensic Science Division.
• Yumiko Cheng as Monique Hau (侯敏莉), a sommelier and Ko On's girlfriend, though they later broke up.
• Gabriel Harrison as Stan Sze (施見賢), a voiceprint expert.
• Kelly Cheung as Emma Ma Oi-mei / Ko Sin (馬愛薇 / 高善)

• William Chu as Ocean Lam (林凱淳), a scientific evidence officer (SEO) from the Forensic Science Division.
• Terrence Huang as Howard Chan (陳浩榮), a forensic technician from the Forensic Science Division.
• Fred Cheung as Ivan Szeto (司徒勳), a forensic pathologist from the Forensic Pathology Division.
• Arnold Kwok as Yu Wai-ding (余偉鼎), an officer from the Kowloon West Regional Crime Unit.
• Fei Wu as Mok King-chiu (莫敬超), an officer from the Kowloon West Regional Crime Unit.
• Wiyona Yeung as Tong Sum-yuet (唐心悅), an officer from the Kowloon West Regional Crime Unit.

• Patrick Tse as Long Siu-tin (龍兆天), the founder of a famous Cantonese Opera troupe.
• Michelle Yim as Long Ying-suet (龍映雪), a famous Cantonese Opera actress and the leader of the Cantonese Opera troupe.
• Nina Paw as So Fong (蘇芳), a mother who sold her daughter because of poverty, but she was regretful and tried hard to find her daughter.
• Mak Ling-ling as Principal Mak (麥校長), a secondary school principal.

When TVB first announced the drama will air in February 2020 which is considered an unpopular time slot, it was expected the drama will receive lower viewership. However, due to the COVID-19 pandemic, Hong Kong went into a strict lockdown in February 2020, which gave viewership ratings a large boost, making the series the most watched drama since 2013.^[5] However, the drama was criticized by audiences for its predictable and average plot compared to its predecessors, especially in the latter half of the series.^[6]