In the Line of Duty IV

A joint task force of the Hong Kong police and the FBI is engaged in an intense investigation into a complex drug smuggling ring that has been operating with apparent impunity. The stakes are raised when an undercover Hong Kong officer is mysteriously killed. Inspector Yeung, a determined and skilled policewoman, and her counterparts take charge of the case, driven to bring the criminals to justice and to unearth the mole within their ranks who could be tipping off the drug lords. The investigation is marked by high-speed chases, martial arts battles, and clandestine operations, emphasizing the dangerous and unpredictable nature of undercover work.

The escalating violence of the criminal group turns personal when it targets the members of the law enforcement task force, leading to a relentless cat-and-mouse game with dire consequences at every turn. Inspector Yeung, along with her new partner from the American force, an expert martial artist with a personal vendetta against criminals, delves deeper into the sordid world of the drug trade. As they confront hitmen and traitors, the line between friend and foe becomes blurred, building tension as trust within the team grows thin. The duo's expert fighting skills and commitment to justice push them to bend the rules of law enforcement in pursuit of their ultimate goal: to dismantle the drug ring and reveal the identity of the traitor.