To infiltrate a drug cartel, police Inspector Chan Ka Kui (Jackie Chan) goes undercover in a Chinese prison. There, he earns the trust of Panther (Yuen Wah), a cartel member, by breaking him out of prison. With the help of another undercover agent (Michelle Yeaoh), they travel to Hong Kong and join up with Panther's gang. Ka Kui is accepted by the gang's leader (Ken Tsang), but his operation is jeopardized when Ka Kui's girlfriend (Maggie Cheung) accidentally reveals his true identity.