During the 1931 occupation of Shanghai by Japan's armed forces, a Chinese resistance group known as Purple Butterfly plot the assassination of Yamamoto, the head of the invading country's secret service. Ding Hui who works for the clandestine organisation in the midst of this city rife with violence realizes that her pre-war Japanese lover Itami has returned to China and reports directly to the assigned target. Can Itami be trusted or will discovery of Ding Hui's identity and mission lead to the death of herself and her freedom fighting comrades?