1999 film by Johnnie To

2006 film by Johnnie To

A reforming ex-gangster tries to reconcile with his estranged policeman brother, but the ties to his former gang are difficult to break.

After working as an undercover in a triad for 8 years, Sheng finally arrests the triad leader and resumes his duties as a police officer. However, life does not return to normal as he is faced with suspicions colleagues and even trailed by the investigations team. One day, he meets some triad members whom he has earlier befriended as an undercover agent and is forced into a corner when asked to collaborate with them once again.

2017 film by Wong Jing and Jason Kwan

2019 film

Based on real-life crimes that terrorized Hong Kong in the 1990s, Logan (Tony Leung Ka-Fai) is the head of leading a notorious human trafficking gang, abducting the children of Hong Kong's elite. Police forces decide to send in Sky (Louis Koo), a Hong Kong undercover agent whose mission is to infiltrate and save the hostages, all while bringing the gang and their leader to justice.