Hong Kong policeman Chia Chu (Jackie Chan) goes undercover in mainland China to bust a drug-smuggling ring and, with the help of undercover agent Jessica Yang (Michelle Yeoh), breaks the drug lord's brother out of prison to gain the trust of the syndicate. But when Chia accidentally runs into his girlfriend, May (Maggie Cheung), his cover is blown, and he's forced to help the criminals pull off another jailbreak.