In 1931, China is embroiled in a civil war. Friends of British Captain Donald "Doc" Harvey (Clive Brook) envy him because the fabulously notorious Shanghai Lily (Marlene Dietrich) is a fellow passenger on the express train from Peking to Shanghai. Because the name means nothing to him, they inform him that she is a "coaster" or "woman who lives by her wits along the China coast" – in other words, a courtesan. On the journey, Harvey encounters Lily, who turns out to be his former lover Madeline. Five years earlier, she had played a trick on him to gauge his love for her, but it backfired, and he left her. She frankly informs him that, in the interim, "It took more than one man to change my name to Shanghai Lily." When Lily clarifies that she still cares deeply for him, it becomes apparent that his feelings also have not changed when she inadvertently sees the watch she gave him with her photograph still in it.