It's 1881 in China's Forbidden City and Princess Pei Pei (LUCY LIU) is sneaking out with her American tutor, Calvin Andrews (JASON CONNERY), to avoid a prearranged marriage to the Prince who's only a young boy. One of her Imperial Guards who's smitten with her, Chon Wang (JACKIE CHAN), wants to stop her from leaving, but instead bows down in complete and utter respect to her authority.
The princess, however, discovers that her tutor is an accomplice to Lo Fong (ROGER YUAN), an ex-Imperial guardsman who kidnaps her in Carson City, Nevada and demands a ransom in gold be paid for her release. Back in the Forbidden City, three Imperial guardsmen are chosen to accompany the royal interpreter (HENRY O) to rescue the princess, and Chon gets to tag along only because the interpreter is his uncle.
Seven weeks later and en route to Carson City, Chon, his uncle and the three guards run into Roy O'Bannon (OWEN WILSON) and his small, ragtag group of outlaws that includes Wallace (WALTON GOGGINS), the hotheaded newest member of the bunch, who ends up shooting and killing Chon's uncle during a train robbery.
After a series of close-calls with those outlaws, some Crow Indians and in a barroom brawl, Chon finds himself not only with an Indian wife, Falling Leaves (BRANDON MERRILL), given to him by a tribal chief for rescuing one of his people, but also an unlikely partner in the form of Roy, an outlaw only in name with an otherwise laidback and harmless demeanor to him.
Learning the ropes of becoming a cowboy and then being deemed an outlaw himself due to his association with Roy, Chon most overcome various obstacles, including that of Marshall Nathan Van Cleef (XANDER BERKELEY) and other men who want to capture or kill him and Roy, all while trying to rescue the princess.