Sensei Yumi is teaching all the pups the ancient art of Pup-Fu. The PAW Patrol and the mischievous kittens from Mayor Humdinger's Kit-tastrophe Crew are both competing for their belts when they come across an ancient scroll that holds all the secrets of the art. Mayor Humdinger steals the scroll and the PAW Patrol is called upon to find and return it to back to Sensei Yumi. It can be dangerous in the wrong hands, so Chase's drone tracks the sneaky Mayor to his secret lair, while Zuma helps them enter by a hidden cave in the water. Super Pup-Fu student Marshall sneaks in quiet as a mouse and together they get the scroll back where it's supposed to be.
The episode begins with Ryder holding up a wooden board. Rubble is shown at the opposite of Ryder and the board, and proceeds to do a number of acrobatic maneuvers before breaking the board with a flying kick. Ryder congratulates him, while Rubble is eager to break another. Ryder suggests he should practice other techniques, while throwing the wooden pieces into a larger pile where Marshall is seen hiding.
Ryder comments to Farmer Yumi that the pups have made a lot of progress in the art of Pup-Fu. Yumi agrees, noting that she is particularly impressed with Marshall, who is learning to be as quiet as a mouse. She goes on to remark that the pups should be ready to earn their yellow belts. At that, Ryder turns to the pups and questions if they heard the exciting news. At this time, it is noticed that Marshall is not among them. While they call for Marshall, he starts sneaking down a pyramid of hay bales, but slips in his non-Pup-Fu ways, and instead ends up riding down on one. When the others ask where he was, Marshall explains that he can sneak around silently and unpredictably. In the meantime, he backs up onto a small catapult, from which Garbie fires him into the wooden pile. The other pups express their concern, but Marshall claims he's fine; though admits he was surprised.
The scene is then shown on a giant screen watched by Mayor Humdinger from inside a cave. Always ready for competition, the mayor laughs as he gloats that the Kitten Catastrophe Crew will earn their yellow belts before the pups do. The kittens' expertise is demonstrated by Cat Chase, as it performs some midair kicks for a pink mouse toy Humdinger holds up.
Back in the barn, the pups are ready to execute their martial arts routines following a brief pep talk from Ryder. Mayor Goodway is also revealed to be present, admiring her “mighty” Chickaletta. At Farmer Yumi's invitation, each pup steps up to perform their individual routines. Before Chase can start his routine, he sneezes due to Cat Skye approaching him. Farmer Yumi is caught off guard and Mayor Humdinger's arrival is signaled.
Mayor Humdinger proclaims that his kittens' Cat-jitsu abilities will put Pup-Fu to shame. Mayor Goodway retorts by supporting Pup-Fu as the dominant martial art, along with Chickaletta's Hen-kido. Farmer Yumi mediates that no art form is superior, as mastering the martial arts is about a collective effort to do one's best – to which the mayors respond competitively.
Without further ado, Farmer Yumi allows the kittens to demonstrate their skills. In sequence, most of them perform, strongly enough to satisfy Mayor Humdinger. Cat Rocky, however, is seen up on the barn's loft, near a rope. Marshall joins the kitten, and says he will show it how to zip line like a Pup-Fu master. While Marshall is sliding down, Cat Rocky bounces the rope, causing Marshall to crash land.
Farmer Yumi proceeds with the sparring portion of the test, and calls up Zuma and Chase. While the pups spar, Mayor Humdinger looks at an ancient scroll, noting its potential value. He is surprised by Farmer Yumi, who confirms the power and value of the scroll by revealing that it contains the most ancient secrets to Pup-Fu. Humdinger leaves the area, and Yumi initiates a sparring match between Marshall and Cat Chase, which results in Marshall getting tangled up by a yarn ball fired from Cat Chase's cannon. Farmer Yumi appears concerned with Marshall's fumble, while Mayor Humdinger laughs.
Farmer Yumi then announces the presentation of the belts. The pups excitedly chatter before Yumi awards them to Chase, Rubble, Skye, Rocky and Zuma. After the five are congratulated (at which they cheer), Marshall whines – having not received a yellow belt of his own. Farmer Yumi silences him and awards him with one, complimenting his hard work. She then turns to Mayor Humdinger and states that his kittens cannot earn their belts until they learn to control both themselves and their gadgets. In shock and anger, Humdinger and the KCC storm out, and Ryder tells the pups how proud he is of them.
At night, while the PAW Patrol is soundly sleeping at the Lookout, Mayor Humdinger returns to Farmer Yumi's barn. Cat Chase opens and enters through a door leading to the loft, and as the kitten jumps through, a pink toy mouse falls on the frame. Cat Chase zip lines down to the bottom level and opens the door for Mayor Humdinger, who promptly grabs the ancient scroll and runs off – the barn doors closing behind him.
In the morning, Ryder gets a call from Farmer Yumi, telling him the scroll had disappeared and that the only clue she had found was the open loft door. Ryder promises her that he will retrieve the scroll, and summons the pups. On the way to the elevator, Marshall dodges many toys strewn about, confidently jumps on a skateboard, and crashes into the elevator with Rubble (who had cut him off). In the observatory, Ryder explains the event to the pups. He calls on Chase to help determine and track down the thief, and Marshall to examine the loft and rafters of the barn for clues.
Arriving at Yumi's barn, Marshall uses his ladder and climbs through the open left door, confused as to why a toy mouse is there. He continues to search for more clues, and instructs the birds following him to do the same. On the ground level, Ryder and Farmer Yumi discuss how Mayor Humdinger was looking at the scroll the day before. With Chase sneezing around the scroll's pedestal, they all deduce that Humdinger and the Kitten Catastrophe Crew had come back the night before, and had likely stolen the scroll. Before the PAW Patrol leaves, Farmer Yumi bestows Marshall with the title of “supreme guardian of the scroll” for his intense dedication towards learning Pup-Fu.
In Foggy Bottom, Mayor Humdinger is found sitting on a bench with his kittens, prepared to open and read the scroll. Before he can accomplish much, he hears the PAW Patrol approaching. Humdinger quickly hides the scroll in the cat carrier and tells the kittens to act naturally as they block the scroll from view. Ryder, Marshall and Chase arrive and relay the story of the missing scroll to Mayor Humdinger, while questioning him and his kittens. Humdinger acts ignorant and declares that the scroll would never be found in Foggy Bottom. Unsatisfied, the PAW Patrol leaves and hides in a nearby area, using the fog as cover. Ryder, Chase and Marshall are skeptical of the mayor's words, especially with Chase having sneezed near the kittens (as he did previously when near the pedestal). Since the team would be too easily spotted following Humdinger, Chase deploys his spy drone.
Believing he is unnoticed, Mayor Humdinger departs on the cat carrier shortly thereafter. The drone follows him to a beach, and the PAW Patrol monitors the relayed video from a rock ledge overlooking the area. Afraid the drone is going to be spotted, Chase gets it to pull up above some clouds, knocking a seagull off its course in the process. The bird resultantly distracts Mayor Humdinger, but by the time the drone is brought back down, he is out of sight. Ryder then calls on the other PAW Patrol members to join them.
Skye is asked to see if she can find Mayor Humdinger. From the air, she cannot find any clues and decides to land on the beach. On the ground, she finds a trail of paw prints. She informs Ryder and he and the other pups meet her down there. They follow the prints until there are no more, and Ryder asks Zuma to get a look from the water. Zuma does so and spots the empty cat carrier next to a nearby area of rocks. With everyone wondering where the KCC could be, Marshall makes a comment that it is as if they disappeared into the rocks. Ryder thinks that may be the case, and while there is no visible doorway, he spots holes within the rock face. Chase calls on his spy drone and sends it in, finding the kittens (to Rubble's contentment), and the scroll.
Mayor Humdinger is found nearby, approaching the rock face. Chase ducks behind him and follows him through a hidden, automatic door. Sneaking around in the cave, Chase eventually gets to the scroll, but before he can grab it, he sneezes. The Kitten Catastrophe Crew quickly reacts and Cat Chase uses the zip line suction cup to grab the scroll. After the kitten passes it off to Cat Rocky, Humdinger and the KCC flee. Chase demands them to stop, but is incapacitated by his cat fur allergy.
Outside, the KCC and Humdinger take off using the cat carrier. Marshall tries to jump down onto them as they pass, but he misses and falls onto the beach sand instead. The PAW Patrol gives chase in its vehicles, with Skye assuring Ryder that Humdinger is still traveling along the beach. When the PAW Patrol gets close to the mayor, he remotely opens the cat carrier's door and Cat Chase shoots out yarn balls from its cannon. Most of the PAW Patrol avoids them, but Rubble spins out. Ryder, Rocky, Chase and Marshall double back to check on Rubble, who is fine (albeit dizzy). Rocky is concerned about them having losing sight of Mayor
Humdinger, but using his sense of smell, Chase confirms that the KCC is still headed in the same direction as before. The PAW Patrol continues its pursuit, and Marshall decides to take a path leading to higher ground.
Feeling victorious, Mayor Humdinger comes to the same bench as earlier in the episode, which Marshall can be seen lurking behind. When Humdinger is prepared to continue reading the scroll, Marshall jumps out and surprises him. After asking the mayor to return the scroll, Humdinger concedes and asks his kittens to give it to Marshall, winking at them. The kittens play keep away with Marshall, but eventually they lose control of the scroll. Marshall is tripped by Cat Rubble's shovel, however still manages to jump and fetch the airborne scroll. Landing on his back at the bottom of a hill, the Kitten Catastrophe Crew surrounds Marshall and assume martial arts stances. While Marshall is worried, the rest of the PAW Patrol arrives and at Ryder's direction, the pups surround the kittens. The kittens fearfully flee to their cat carrier and take off, with Mayor Humdinger chasing and later hopping onto it, calling them cowards.
Back at the Lookout, the PAW Patrol celebrates the return of the scroll with Farmer Yumi, Mayor Goodway and Chickaletta. Farmer Yumi presents a golden belt with a dragon symbol on it to Marshall for his bravery and dedication, while Mayor Goodway draws attention to Chickaletta, who is now capable of breaking boards with a single peck.