In the international settlement of Shanghai, the Suzhou River seems to separate the old Shanghai's romantic and luxurious lifestyle from the new Shanghai's decadent and extravagant one. Ma Da rides a motorcycle across the Suzhou River to deliver goods for people. One day, his "cargo" happens to be an innocent young girl named Mu Dan (played by Zhou Xun). Over time, they fall in love with each other. Unexpectedly, one day he kidnaps her and demands money. Upon discovering this, Mu Dan angrily jumps into the Suzhou River, leaving behind a sentence: "I will become a mermaid and come back to find you!"
After Ma Da is released from prison, he meets a girl in a bar who looks exactly like Mu Dan. She earns a living by dressing up as a blonde mermaid in the bar, and her name is Mei Mei (also played by Zhou Xun). But Mei Mei claims that she doesn't remember anything about Ma Da or Mu Dan. Is she really the Mu Dan who drowned herself in the river?