"'Who are you?' you must be wondering. I am your soulmate, your old friend, and I have come back to this city of sixteen million in search of you." So begins the first letter that falls into Wang's lap as he flips down the visor in his taxi. The letters that follow are filled with the stories of Wang's previous lives -- from escaping a marriage to a spirit bride, to being a slave on the run from Genghis Khan, to living as a fisherman during the Opium...