Cynthia (Zhang Ziyi) and a Japanese student, Itami (Tôru Nakamura), have fallen in love in Japanese controlled Manchukuo prior to the war when Itami is forced to return to Japan.
Years later, in Shanghai, Szeto (Liu Ye) and Tang Yiling (Li Bingbing) have fallen in love. Cynthia has also returned to Shanghai now as a member of Purple Butterfly, a powerful resistance group against the Japanese occupation, led by Xie Ming (Feng Yuanzheng). After a case of mistaken identity and a shootout at a railroad station that leaves Yiling dead, Szeto finds himself an unexpected pawn in the battle between former lovers Cynthia and Itami who has also come to Shanghai, now as a member of the Japanese secret police unit tasked with dismantling Purple Butterfly. [Wikipedia]