上海苏州河上，用摩托车替人送货的马达（贾宏声）接下送接纯真少女牡丹（周迅）的活，两人相处时，牡丹爱上马达，但就在她决定把终身托付给对方时，马达财迷心窍联合黑道朋友绑架了她，令牡丹心灰意冷跳进苏州河里。临跳前，牡丹丢下会变成美人鱼再寻马达的话。 　　五年后，为自己行为懊悔不迭的马达疑惑牡丹又回来了，开始四处找寻。当在某酒吧里看到扮美人鱼表演的美美（周迅）时，马达认定她就是牡丹，然而美美不过是另一个痴情女子而已。The river Suzhou that flows through Shanghai is a reservoir of filth, chaos and poverty, but also a meeting place for memories and secrets. Lou Ye, who spent his youth on the banks of the Suzhou, shows the river as a Chinese Styx, in which forgotten stories and mysteries come together. Mardar, a motorcycle courier in his mid-twenties, rides all over the city with all kinds of packages for his clients. He knows every inch and is successful thanks to the fact that he never asks questions. One day he is asked by a shady alcohol smuggler to deliver his sixteen-year-old daughter, Moudan, to her aunt. Mardar and Moudan grow fond of each other. But their tender happiness is disrupted when Moudan thinks that Mardar has kidnapped her for a ransom. She is so disappointed in him that she jumps off the bridge into the Suzhou River. Mardar is now suspected of murder. When a couple of years later he comes out of jail, he meets the dancer Meimei, an alter-ego of Moudan, and becomes fascinated by her.