We see a flashback: The Demon Bull King surfaced from the Netherworld and terrorized the villages. Monkey King was the only one powerful enough to stop him. He sealed the Demon Bull King underneath a mountain with his staff for many years, vanishing. Legends say the staff still remains atop that mountain, keeping the world from descending into total annihilation. Thanks to the Monkey King, civilization advanced and a city arose, home to a plethora of diverse people, cultures, and cuisines.
MK is invigorated by the story Tang just told him, and goes on to fanboy about the Monkey King some more, describing him as "cool", "strong", and "handsome". Tang shrugs him off, saying that he thought MK knew all about the Monkey King. MK reveals he was working on an unauthorized autobiography of the Monkey King, to which Tang expresses that he is proud of MK being so drawn towards the legends. He then reminds MK of their deal: "one story, one free bowl of Zha Jiang Mian (a traditional Chinese noodle dish with bean curd sauce, typically served with cucumbers)". As he is about to eat, MK wonders how heavy a mountain is. Pigsy freaks out over the aspect of free noodles, and goes into a rant about how no one gets a free meal on his watch. Tang tries to calm him down with the idea of having wisdom be the payment rather than money, but Pigsy ignores him. MK then informs Pigsy that he was about to take his break, but Pigsy denies him the permission, instead of ordering him to make the shop deliveries.
MK heads out and follows a delivery order to a dark construction site, where Red Son and Princess Iron Fan are attempting to free the Demon Bull King from the mountain Monkey King imprisoned him in. A Bull Clone named Bob tries to pull the staff out, but ends up losing his arms. MK spies on the whole thing from above, accompanied by a bird. Red Son then uses a gauntlet to pull the staff from the earth, successfully freeing the Demon Bull King. The bird then pecks at MK's hands, causing him to fall onto Red Son and into view. The Demon Bull Family tries to attack him, but MK desperately uses the staff in self-defense, which saves him and helps him escape the construction site.
Red Son gives pursuit, but MK is then rescued by a mysterious green motorcycle rider, later revealed to be his childhood friend, Mei. Meanwhile, Red Son returns in defeat but manufactures an armor for his father that will absorb rare items and convert them into energy. Back at the noodle shop, MK attempts to explain what happened to his friends, but none of them believe him, not until he splits a table with the staff. The group then finds out that the Demon Bull King has robbed a shoe store and is powering up himself in order to reclaim the staff.
The team then decided to seek help from the Monkey King himself on Flower Fruit Mountain. However, Tang pointed out that the journey to the mountain would be dangerous, thus Pigsy insists that they would seek aid from one of his old friends, a reformed peace-loving warrior named Sandy. he takes them to the mountain on his barge while MK practices with the staff, but on the way to the mountain, they are stopped by Princess Iron Fan, who uses the gauntlet to steal back the staff and seemingly kill MK, launching him into the fiery rocks just before the mountain. Swearing to avenge him, Mei, Pigsy, Tang, and Sandy return to the city to face the Demon Bull King.
Meanwhile, MK is shown to have survived, making it to Flower Fruit Mountain. He is led by a pack of white monkeys to a waterfall. As MK enters the waterfall, he comes across a wall of paintings depicting the multitude of adventures the Monkey King and his gang went on. Whispers of "Sun Wukong (Monkey King's Chinese name)" can be heard in the background. MK then chases an illusion of Monkey King, only to pass right through him and leading him to a small shack. He at first believes all his efforts were for nothing, but just then, a butterfly flies down, changing into an eagle, then a tiger, and then finally, his true form, which is the Monkey King himself. MK explains what has happened thus far, but Monkey King reveals to already know, as he had been watching him. He then tells MK that it's up to him, saying he needs only to believe in himself to win.
Back in the city, Pigsy drives the gang to confront the Demon Bull King, but they are halted by Red Son. Mei is about to face off with him when MK makes his triumphant return, riding a jet he found in one of Sandy's shipment containers. He takes out Red Son and reunites with his friends. He passes on Monkey King's message and goes straight into Demon Bull King's armor to retrieve the staff. Emerging with said staff in toe, he forms the Monkey Mech and defeats the Demon Bull King for the moment before Princess Iron Fan retreats him and the rest of their troops. The group then decides to celebrate with some noodles (at the suggestion of Mr. Tang) as Monkey King watches on proudly.