Cloud city - the paradise for the soul of the departed. Here, the souls lives after life on paper offerings from human family. Only on lunar July 15, when the gates of hell open. The deceased can use paper money to buy tickets back to the earth to see and interact with loved ones. 

There is a mother living in the cloud city, but she has not received the money from her son for many years. So she decided to take out the only left coin to go back to the earth to see what has happened to her son.

When she's down to the earth, she found her son unhappy, overworked, and the pollution of the environment has made the happy boy sallow and emaciated. The love pushes the mother to teach her son what is the true meaning of life.