Two detectives who are up to their necks in trouble and in each other's face, as they try to shut down a drug-trafficking scheme that could be connected with international ties to organized crime. But in the midst of their investigation, innocent immigrant dock worker Luk Wan-Ting gets caught up in the mix when he witnesses the murder of an intelligence operative and is framed for the crime.
You can now watch In the Line of Duty 4 online on the following streaming providers in the United States.
| Directing | Yuen Woo-Ping | Director |
| Writing | Wing-Fai Wong | Writer |
| Writing | Cheung Chi-Sing | Writer |
| Writing | Kim Yip Kwong-Kim | Writer |
| Writing | Stephen Shin | Writer |
| Crew | Yuen Woo-Ping | Martial Arts Choreographer |
| Crew | Yuen Shun-Yi | Martial Arts Choreographer |
| Crew | Paul Wong Kwan | Martial Arts Choreographer |
| Crew | Cho Wing | Martial Arts Choreographer |
| Production | Dickson Poon Dik-Sang | Executive Producer |
| Production | Stephen Shin | Producer |
