This is a religious story which is usually performed during celebrations for Buddha's birthday or other religious festivals.
Mu Lian is one of the ten great disciples of Buddha. He has been born into a wealthy family, and his parents are happy to be associated with Buddhist monks. They often help the poor and enjoy doing charitable works. After Mu Lian's father passes away, Mu Lian decides to become a monk and to study Buddhism in the temple. He says goodbye to his mother Liu Qingti and leaves home. Following his departure, his mother begins to kill animals and eat meat products under the influence of Mu Lian's younger brother. She also grows impatient towards the monks who come to her house for food. She soon dies unexpectedly.
Mu Lian thinks his mother is already in Heaven, so he goes to the Western Paradise to seek his mother. After he crosses the Milky Way, he rids himself of his human shape and becomes a free spirit. When Mu Lian arrives at Mount Lu, Buddha informs him that his mother has been detained in Hell, and that she is standing trial at that moment. Mu Lian wants to save her from Hell, but since he is now a free spirit, he is unable to open the gates of Hell. He thus returns to Buddha and asks for instruction. Buddha admires his devotion and presents him with a magic stick as a gift.
In Hell, Mu Lian passes through many obstacles and endures challenges from many ghosts before he finally finds his mother. He breaks through layers and layers of Hell's curses with his mother on his shoulder. They finally return to the world above. His mother recognizes her sins and corrects her wrongdoings. Mu Lian then is rewarded as one of the greatest disciples of Buddha for his devotion to his mother.