The film opens in Japan. The Japanese cop, Takami (Kenya Sawada) visits the graves of his team mates, viciously slaughtered when their SWAT team attempted to engage the terrorist group Shojenomichi. In flashbacks we see how the mission went wrong and how one of his men with his dying breath asks Takami to track down and capture the Shojenomichi leader Yoshinaga.
Cut to Hong Kong. Detective Ken Cheung (Julian Cheung) visits the television station where his girlfriend Anita Lee (Shu Qi) works. On the way home, they witness a group of armed men attacking a truck with chemical supplies. They remove some containers from the truck and kill the driver. Ken manages to take control of the truck and avoid a major accident (sure, the truck still blows up, but it could have been worse!). When the traffic cops arrive at the scene, they write the incident off as a simple accident. But Ken knows better and he suspects something serious is on the way.
Meanwhile Ken's boss and one of his colleagues (Theresa Lee) wait for him at the Japanese consulate where a meeting has been arranged between the Hong Kong and Japanese police departments. When Ken finally shows up for the meeting, we learn that Hong Kong police has just captured Yoshinaga, but the Japanese wants him extradited, because he's up for the death penalty in Japan. Takami is present at this meeting and explains to the HK police that they have no idea who they are dealing with.
The next moment Yoshinaga's second in command, Takizawa Ryuichi, shows up at the consulate. He murders Ken's boss, and tells the Hong Kong police they have 24 hours to hand over Yoshinaga, or else Hong Kong will be destroyed in a giant serine gas explosion. Ken and Takami now both have things to avenge, and they begin to work together to find the Shojenomichi group and stop their plans. Ken suspects that the chemical heist earlier in the day may have something to do with the Shojenomichi group and they attempt to track down the the laboratory where the chemicals are concealed, but they arrive a moment too late.
The Shojenomichi group already has their deadly serine gas and they embark on the next step of their plan: They attack a TV-station in the middle of Hong Kong and take all the employees hostage. This way they can address the media, and they have the perfect place to launch the gas. Unfortunately this is the same TV-station that Ken's girlfriend works in...