The all-powerful Monkey King, Sun Wukong, is imprisoned by the Buddha within an ice cage deep within the mountains for rebelling against heaven.
500 years later, Mountain Trolls attack a group of travelers, all except for a baby boy named Liuer are killed, and Liuer is adopted by a monk after floating down a river in a basket. (The name Jiang Liuer means River Flow Child.) Several years later, the same trolls invade a small village and kidnap 49 young children. Liuer saves one of the baby girls and is chased by the trolls for doing so. He stumbles into the cave where the Monkey King was imprisoned, and unknowingly releases him from his curse. Sun Wukong defeats the trolls, although he is only able to use physical attacks, since a remnant of Buddha's seal prevents him from regaining his magical powers, causing him pain whenever he tries to harness his magic.
Wukong attempts to break the Buddha's seal to no avail. Liuer and the girl enthusiastically greet Wukong, not knowing he has lost his powers, and pester him with endless questions. (One example is when Liuer asks if the god Nezha is a boy or a girl. Wukong answers, a girl.) Annoyed, Wukong attempts to avoid the two, but is unable to evade them. A stone monster, created by the Buddha to keep Wukong imprisoned, attacks the three. Liuer manages to undo the spell on the monster, but falls off a cliff in the process. When he awakes, he finds out Wukong has saved him.
The three come upon Pigsy, the Heavenly Immortal "Tian Peng Yuan Shuai" (Marshal of Heavenly Canopy) that Wukong defeated when he rebelled against Heaven 500 years ago, now reincarnated into a pig demon. Though Wukong is again hesitant, Pigsy joins the group as well. They also run into a white dragon that attacks them and tries to eat Liuer but Sun Wukong scares it off. (This also happened in the original canon, although unlike in the original books, the dragon does not turn into a white horse.)
They stay overnight at an inn, but its owners turn out to be Trolls in disguise, who try to kidnap the baby. More trolls arrive and Wukong fights them off. The leader of the monsters, Hun Dun, appears, defeating Wukong and capturing the girl. After Wukong refuses to pursue them, Liuer goes ahead to save them on his own.
Hun Dun reveals his plan to sacrifice all the children they have kidnapped in order to gain magical powers. Liuer meets with his mentor, Fa Ming, to try to rescue them but nearly get captured. Wukong finds a doll of himself that Liuer had and realises how important of a figure he is. He and Pigsy go to help Liuer. Saving Liuer and the 49 children, Wukong defeats the monsters. However, a solar eclipse occurs, and Hun Dun turns into a giant monstrous beast. Liuer is seemingly crushed by the rubble from Hun Dun's rampage. Upon seeing the boy's apparent death, Sun Wukong is devastated. Full of fury, he forcibly breaks Buddha's Seal, regaining his original supernatural powers, and easily defeats Hun Dun.
The final part of this movie connects to the themes in the original canon. Sun Wukong only regains his powers when he fights for someone else rather than himself, as Sun Wukong's powers are meant to protect the monk Xuanzang/TangSeng/Tang Sanzang against evil and lead the monk to enlightenment. Sun Wukong as a character is also meant to represent an enlightened mind, which is why Sun Wukong's staff emerges from his head. Jiang Liuer himself is the younger Xuanzang, since he only received the name Xuanzang after he was ordained.
In the end, Liuer is shown to have survived Hun Dun's rampage, and they return the abducted children to their families.
On October 17, 2019, a video game based on the film was released on PlayStation 4, developed by HexaDrive with assistance from Japan Studio and published by Sony Interactive Entertainment in Asia and THQ Nordic internationally; a Windows port published by Oasis Games was also released on the same day.[12][13] As Sun Wukong (renamed Dasheng in the English dub), players guide Liuer and Pigsy (Zhu Bajie) to fight off Mountain Trolls and other monsters to save the kidnapped children from the clutches of the demon king Hun Dun, use statues of Guanyin to unlock spells to enhance skills and use various weapons to battle enemies. Two DLCs were available: Mind Palace, which is set within Sun Wukong's mind sealed inside the Buddha's crystal, where he trains himself in a series of obstacles and traps between different biomes, and Uproar in Heaven, which is set before the main story where the monkey king duels against three of the Jade Emperor's greatest warriors, Nezha, Juling Shen and the Jade Emperor's nephew Erlang Shen.
The film crosses over with other animated films such as Ne Zha and Jiang Ziya in various commercials.
