A Supplement to the Journey to the West is a Chinese shenmo (fantastic) novel written around 1640 AD by Dong Yue. It acts as an addendum to the famous 16th century novel Journey to the West and takes place between chapters 61 and 62. The novel contains 16 chapters.

In the story, the Monkey King is trapped in a dream world by the Qing Fish demon, an embodiment of desire, who wishes to eat his master, the Tang Sanzang. He wanders from one adventure to the next, using a magic tower of mirrors and a jade doorway to travel to different points in time. In the Qin dynasty, he disguises himself as Consort Yu (Xiang Yu's wife) in order to locate a magic weapon needed for his quest to India. During the Song dynasty, he serves in place of King Yama as the judge of Hell. After returning to the Tang dynasty, he finds that Tang Sanzang has taken a wife and become a general charged with wiping out desire. In the end, Monkey unwillingly participates in a great war between all the kingdoms of the world, during which time he faces one of his own sons on the battlefield. He eventually awakens in time to kill the demon, thus freeing himself of desire.

At the end of the novel, the author lists twelve hypothetical questions that a reader might ask and answers them. For instance, he explains that the reason he wrote the Supplement is because he wanted Monkey to face an opponent—in this case desire—that he could not defeat with his great strength. He also explains why he waited to reveal the monster at the end of the novel, why Monkey serves as King Yama, and the peculiarities of time travel in the dream world.

There is a debate between scholars over when the book was actually published. One school of thought favors a political interpretation which lends itself to a later publication after the founding of the Qing dynasty (1644–1911). The second favors a religious interpretation which lends itself to an earlier publication during the late Ming dynasty (1368–1644). Evidence in favor of the former includes references to the stench of nearby “Tartars,” a possible allusion to the Manchus who would eventually found the Qing dynasty of China. Evidence in favor of the latter includes references to Buddhist sutras and the suppression of desire and the lack of political statements “lament[ing] the fate of the country.” The novel can ultimately be linked to the Ming because a mid-17th century poem dates it to the year 1640.

The novel draws heavily from Yuan and Ming dynasty tales, including the literary ancestor of the Romance of the Three Kingdoms. Modern literary critics also noted the novel's use of stream of consciousness technique as innovative and trailblazing.

Plot

During the battle with the Rakshasi Lady Iron Fan, Monkey transforms into an insect and enters her stomach. He forces her to give him the magic fan that he needs to quell the heavenly fire of the Flaming Mountain blocking their path to India. However, while he is in her stomach he becomes aroused with passion. This becomes a chink in Monkey's emotional and spiritual armor as he is otherwise without weakness. It is months after the pilgrims bypass the mountain that he falls prey to the magic of the Qing Fish demon, an embodiment of desire. The demon uses its powers of illusion to trap him in a dream world so nothing will keep it from eating the Tang Priest. The story from this point reads disjointedly as the dream world does not adhere to the rules of the physical world.

While on a mission to find food, Monkey comes upon a large city flying the banner “Great Tang’s New Son-of-Heaven, the Restoration Emperor, thirty-eighth successor of Taizong.” This strikes him as odd as it was Taizong who had originally sent them to retrieve the Buddhist scriptures in India. This means that either the pilgrims’ journey has taken hundreds of years, or the city is a fake. He flies to heaven in order to learn more about the Great Tang, but finds that the gates are locked because an imposter Monkey has stolen the Palace of Magic Mists.

The situation becomes stranger when he returns to the city and learns that the king has sent someone to invite the Tang Priest to become a general of his military. But when Monkey tries to intercept the messenger, the person is nowhere to be found, and he instead comes upon mortal men flying on magic clouds picking at the foundations of heaven with spears and axes. From them he learns that Little Moon King (), the ruler of the neighboring Kingdom of Great Compassion, has put up a great bronze wall and a fine mesh netting to block Monkey's path to India. But because he feels sorry for the Tang Priest, the Little Moon King forced the men to dig a hole in the firmament of heaven so that Tang Sanzang could hop from the Daoist heaven to the Buddhist heaven to complete his mission. In the process, the men accidentally caused the Palace of Magic Mists to fall through to earth (the reason heaven blamed it on him).

Monkey goes to the Emerald Green World, Little Moon King's imperial city, to fetch his master, but is blocked from entering once inside the main gate. When he uses his great strength to break open the wall, he falls into a magic tower of mirrors, gateways to different points in history and other universes. Monkey travels to the “World of the Ancients” (the Qin dynasty) by drilling through a bronze mirror. He disguises himself as Beautiful Lady Yu, concubine of King Xiang Yu of Chu, in order to retrieve a magic “Mountain-removing Bell” from the first Qin Emperor so that he can use it to clear the group's path to India of any obstacles blocking their way. But Monkey later learns that the Jade Emperor had banished the emperor to the “World of Oblivion,” which lies beyond the “World of the Future.” Xiang Yu takes him to a village housing a set of Jade gates that lead to the World of the Future. Monkey leaps through and travels hundreds of years forward in time to the Song dynasty.

After resuming his normal form, some junior devils appear and tell him that King Yama has recently died of an illness and that Monkey must take his place as judge of the dead until a suitable replacement can be found. He ends up judging the fate of the recently deceased Prime Minister Qin Hui. Monkey puts Qin through a series of horrific tortures, after which a demon uses its magic breath to blow his broken body back into its proper form. He finally sends a demon to heaven to retrieve a powerful magic gourd that sucks anyone who speaks before it inside and melts them down into a bloody stew. He uses this for Qin's final punishment. Meanwhile, Monkey invites the ghost of Qin's victim Yue Fei to the underworld and takes him as his third master. He entertains Yue until Qin has been reduced to liquid and offers the general a cup of the Prime Minister's "blood wine." Yue, however, refuses on the grounds that drinking it would sully his soul. Monkey then does an experiment where he makes a junior devil drink of the wine. Sometime later, the devil, apparently under the evil influence of the blood wine, murders his personal religious teacher and escapes into the "gate of ghosts," presumably being reborn into another existence. Yue Fei then takes his leave to return to his heavenly abode. Monkey sends him off with a huge display of respect by making all of the millions of denizens of the underworld kowtow before him.

After leaving the underworld, Monkey is able to return to the tower of mirrors with the help of the New Ancient, a man who had been trapped in the World of the Future for centuries. However, when he tries to leave the tower through a window, Monkey becomes entangled by red threads (a representation of desire). He becomes so worried that his own spirit leaves his body and, in the guise of an old man, snaps the threads. He later discovers from a local Daoist immortal that the Qin Emperor has loaned the Mountain-removing Bell to the founder of the Han dynasty, his former enemy. In addition, he learns that the Tang Priest has given up the journey to India, dismissed his other disciples Pigsy and Friar Sand, taken a wife, and accepted the position as a general of the imposter Great Tang's military. Tang Sanzang begins to amass a huge army to fight the forces of desire led by King Paramita (Perfection), one of Monkey's five sons born to Lady Iron Fan. Monkey is eventually made a junior general and faces his son in battle. Confusion sets in causing the clashing armies to attack both friend and foe. This shock causes Monkey to slowly wake from the dream.

Somewhere between the dream world and the world of reality, he learns from the disembodied Master of the Void that he has been bewitched by the Qing Fish demon. Monkey and the Qing Fish have a connection because they were born at the same time from the same primordial energies at the beginning of time. The only difference is that Monkey's positive Yang energy is offset by the demon's far more powerful negative Yin energy. The demon is in effect the physical embodiment of Monkey's desires. When he finally awakens, having dreamed the entire adventure in only a few seconds, he discovers that the demon has infiltrated the Tang Priest's retinue by taking on the form of a young and beautiful Buddhist monk. Monkey instantly kills him with his iron cudgel, thereby killing his desire. He explains everything that has transpired, and the Tang Priest commends him for his great effort.

Questions and answers

At the end of the novel, the author lists twelve hypothetical questions that a reader might ask and answers them. Some of the answers are very similar in nature and, sometimes, contradictory.

The first question asks whether a supplement was even necessary since the original novel did not seem to be incomplete. He explains that it was written so Monkey would face an enemy—in this case desire—that he could not defeat with his great strength. By experiencing desire he learns to separate himself from it, thus helping to bring about true enlightenment.

The second asks why he faces a single enemy who tricks him with magic, instead of many who want to eat the Tang Priest. The author answers this question with a quote by the philosopher Mencius: “There is no better way of learning than to seek your own strayed heart.”

The third asks why Dong waited to reveal the monster Monkey faces at the end of the novel, instead of doing so in the title of one of the chapters like in the original. He states that desire is formless and soundless, meaning people can be affected by it without knowing it. Therefore, the Qing fish monster is present throughout the entire book.

The fourth asks how it's possible for the spirit of Qin Hui, who lived during the Song, to be in the Tang dynasty. Dong points out that anything is possible in a dream.

The fifth asks why Monkey becomes the fearsome King Yama in the future. He explains a person who travels to the future must embolden their spirit when facing adversity. By killing the six thieves, torturing Qin and honoring Yue, Monkey is able to break free of the Qing fish's power.

The sixth asks why the Tang Priest becomes a general. He becomes a general to wipe out the forces of desire.

The seventh indirectly asks why the Tang Priest cries when a young girl plays the pipa. Dong quotes the Buddhist tenet that sorrow is the source of desire.

The eighth asks how it's possible for Monkey to have a wife and children. He states that the book is simply a dream.

The ninth asks why a chaotic battle erupts between the five armies after Monkey escapes from inside the Qing fish. It's because the accumulation of desire reaches the breaking point. It can be likened to being forced awake during the worst part of a nightmare.

The tenth asks why Monkey is able to escape the dream world just by participating in combat. Dong says combat is how he kills his desire.