In this fourth 'Police Story' movie, Hong Kong 'supercop' Inspector Jackie Chan Ka-Kui (Jackie Chan) is hired by the CIA to follow leads of a nuclear smuggling case. He follows a woman named Natasha to Ukraine, when he realizes that she had been hiding vital information. When Jackie calls for backup, she is arrested. However, Natasha's partner is an unknown man, who turns out to be Tsui (Jackson Lau), a Chinese American nuclear scientist with CIA links, suspected of stealing a nuclear warhead. Jackie follows Tsui to a restricted area, and after a trap set by Tsui, CIA agents together with Ukrainian authorities engage in battle. Jackie finds a briefcase which contained evidence that Tsui had, but as he is chased by unknown forces, he loses the briefcase as he falls through a frozen lake into the freezing water.
When he recovers in Russia, he meets Colonel Gregor (Yuri Petrov) who explains the situation. Jackie goes with the FSB and is taken to Moscow where he discovers he's been assigned to work with Colonel Gregor to solve a similar case involving nuclear weapons being smuggled out of Ukraine. His task is to track Tsui, who disappeared after their last encounter.
Jackie is taken by a Russian submarine to Brisbane, Australia, where Tsui's attractive younger sister Annie Tsui (Annie Wu) works at an aquarium doing shark shows. Uncle 7 (Terry Woo), the Tsuis' father and the local Triad boss, is seriously ill, and Chan suspects the criminal will show up soon. Unbeknown to Jackie, Tsui is hiding at the hospital, and has given a nuclear warhead to Annie, who hides it at the aquarium.
Whilst following Annie, Jackie gets to meet the aquarium animals and is kidnapped by Tsui, who claims to have a deal with Colonel Gregor. Jackie, after realizing he has been used by Gregor decides to return home, but two toughs are sent to kill him, and he is framed for the murder of Uncle 7. He attempts to clear his name by going to see Annie at the memorial hall, but he is (unsurprisingly) unwelcome, having to fight bodyguards and Tsui has to eventually rescue him. Tsui explains that Gregor caught him on a CIA assignment three years before, and forced him to turn into a triple agent: a CIA agent ostensibly turned by the FSB, but in reality serving Gregor's private criminal schemes.
Annie, Jackie and Tsui decide to work together to fight Gregor. Uncle 7's elaborate Chinatown funeral then becomes the scene for a complex showdown between the various parties. Annie and Jackie attempt to retrieve the stolen warhead from the shark pool (so that they can return it to the police), but Gregor and his toughs follow them, leading to a climatic confrontation underwater. In the midsts, Gregor attacks the aquarium and shatters the aquarium glass which releases the killer shark, which makes a good diversion for him to escape. Jackie then saves the tourists and follows Gregor. While Gregor escapes with the weapon and Annie as hostage in a getaway boat, Jackie comes up with an unusual plan that allows him to recover the weapon and return it to the proper authorities, while Annie makes her escape, in which he drives and launches a display car onto the boat.
Gregor and Tsui are apprehended by Australian police and turned over to Russian authorities. The case is solved, Jackie is thanked for his work by the FSB, and the film ends as he returns to Hong Kong.
As is usual in Jackie Chan's films, out-takes (generally accidents involving the star) are shown under the closing titles.