香港国际警察杨丽清(杨丽清 饰)前往美国与当地的缉毒组组长东尼(甄子丹 饰)一起调查西雅图的一起贩毒案,当他们追查到当地的一名华人嫌疑人六仔(袁日初 饰),早已收到消息六仔潜回了香港,于是,杨丽清和东尼一起回到了香港。在追捕过程中,他们发现六仔不断受到追击,几次险些丧命。东尼开始觉得六仔绝对不仅仅是牵涉到这起贩毒案这么简单。当东尼和杨丽清一直追查下去时,发现整件事竟然关系到美国中央情报六局,而东尼的同僚另一组的组长迈克尔(王敏德 饰)竟然也牵涉在内。事件的真相真正一层层剥开。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 mist 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. After escaping police custody and after his friend is brutally killed by hired assassins in search of a film negative that Luk lost, he has no choice but to return to Hong Kong until the heat cools off. Donny and Penny Yeung are called in to extradite him with the aid of Captain Michael. Penny believes that Luk is innocent and tries to do everything in her power to help him, while Donny who is skeptical about Luk's innocence, thinks he's guilty and does his best to snap the cuffs on him. As the two do more investigating, they learn that the drug cartel could have connections with rogue C.I.A. operatives, who could also have someone on the police force keeping tabs on them about their investigation. At this point, Penny and Donny don't know if they can trust their own co-workers or even each other for that matter and Luk's testimony to what he saw poses a threat to the criminals involved in the conspiracy. Now for the next 72 hours, Penny and Donny will have to learn to tolerate each other while trying to protect Luk from the assassins who want him silenced. If they can do that, the bad guys don't stand a chance and they just might all survive this case...if they don't end up killing each other first!