The Equation of Love and Death Neurotic cab driver LI Mi has been searching high and low for her fiance who disappeared four years ago, but continues to send her letters. She carries pictures of him everywhere so she can ask her passengers whether they have seen him. Small-time criminal Qiu has come to the big city to make quick cash and find the woman he loves. Recovering druggie Fei-fei is trying to start anew with her boyfriend. A mysterious death suddenly throws these seemingly separate lives together, revealing their unexpected connections to each other and a drug trafficking case.