Undercover cop Kit (Wu Jing) becomes a junkie in order to catch Mr Hung (Louis Koo), the mastermind behind a crime syndicate. When the operation goes sour and Kit blows his cover, his supervisor and uncle Wah (Simon Yam) decides to terminate the operation. When Kit disappears without a trace, Wah defies the order from his commanding officer and tracks Kit to a prison in Thailand. Thai Police officer Chai (Tony Jaa) becomes a prison guard in order to raise money for his daughter who has leukemia. Hes assigned to keep an eye on Kit. Even though Chai and Kit are in opposing positions and they dont speak a common language, Kit turns out to be a suitable bone marrow donor who can save Chais daughter. While Chai is determined to keep Kit alive, the warden Ko (Zhang Jin) wants him dead to ensure the smooth operation of the prison, which is the front for Mr Hungs organ trafficking business. Mr Hung shows up in Thailand so he can use his younger brothers (Jun Kung) heart in a heart ...