At the Lookout, Chase is practicing for an upcoming mission in the city of Barkingburg, to protect the Crown of Barkingburg. Once he's ready, he and Ryder leave Adventure Bay in the Air Patroller and head for Barkingburg. Meanwhile, in Barkingburg, the Earl of Barkingburg is displaying the crown to the Princess of Barkingburg, saying how she'll be able to wear it when she comes of age to become Queen. Unknown to either of them, the Princess' pup, Sweetie, is planning on taking the crown herself.
Once the Air Patroller arrives over Barkingburg, Chase deploys, and after cruising around Barkingburg and taking in the sights, including Big Benji, Barkingburg's version of Big Ben in London, he arrives at Barkingburg Castle, where after crash-landing, he reappears, now sporting a fancy tuxedo and bow tie. After being introduced to the Princess of Barkingburg, her guardian, the Earl of Barkingburg, and the Princess' pup, Sweetie, Chase is left to guard the crown as the Earl activates the security system and he and the Princess retire to bed.
That night, Sweetie lures the royal kittens out towards Chase, causing his allergies to go off and knock him back into the security lasers, triggering the alarm. As Chase panics and attempts to turn the alarm off, Sweetie uses the distraction to steal the crown. When the Earl and Princess arrive upon being awoken by the alarm, they are shocked to find the crown missing. However, his sinuses clearing up, Chase begins picking up the thief's scent, and tracks down Sweetie, shocked to see she's the thief. After Sweetie reveals that she plans to frame Chase for the theft and be rewarded for retrieving the crown by the Princess and Earl, Chase refuses to let that happen and attempts to summon Ryder and the rest of the team for backup, but Sweetie disarms him of his bow tie pup-tag and opens a trapdoor under him that locks him in the dungeon. With Chase out of the way, Sweetie returns to complete her plan of framing Chase for the theft. Once she tells the Princess and Earl that Chase is the thief, the Earl calls Ryder.
When Ryder learns of this, he refuses to believe Chase has turned to the wrong side of the law, and summons the pups to the Air Patroller. After Marshall declares himself the King of Wipeouts, getting a laugh from Skye, Rubble, Rocky, and Zuma, they climb aboard the Air Patroller. Once on-board, Ryder decides that to find the Crown of Barkingburg and prove Chase's innocence, it is time for the PAW Patrol to enter Mission PAW mode. Cloaking the Air Patroller in its stealth mode, the Air Patroller assumes darker colors, and the propellers withdraw into the engines, making the Air Patroller able to rocket away to Barkingburg at well over Mach 1 with the jet engines.
Once in Barkingburg, the Air Patroller descends into the Mission PAW command center located underground/underwater, where the team climbs out and into an elevator that, unlike the one at the Lookout, descends further into the hideout, suiting the pups, and Ryder, in their new Mission PAW suits and equipment. Once in the briefing room, Ryder uses his wristwatch Pup-Pad to assign orders: Marshall will use his new hydro-launcher to help cut open anything that blocks their way, while Rocky will use his new radar system to help as well. Robo-Dog soon arrives in the Mission PAW Cruiser, which is loaded up with Chase, Rubble, and Skye's new mini-vehicles. Ryder and the pups climb aboard, and the cruiser departs the Mission PAW hideout, emerging into the streets of Barkingburg from underneath a statue in the city square.
When they arrive at the castle, Sweetie realizes that Chase still managed to warn Ryder before she disarmed him, and with Chase's bow tie equipped with a homing device, she realizes that she'll need to lure the PAW Patrol on a wild goose chase to give her time to complete her plan. Stashing the bow tie in a gargoyle statue on the castle's highest tower, she then tries to buy herself more time by knocking over several suits of armor on Marshall, but thanks to Rubble's new Mission PAW construction claw helping Marshall out of that delaying tactic, she's forced to drop Chase's bow tie into the moat to divert the PAW Patrol again while bolting the door to the turret shut for more time, forcing Marshall to cut the lock off with his hydro-launcher while she manages to return to the Princess and Earl with the crown and lies that she got it back from Chase. Falling for it, the Princess rewards Sweetie with the crown for the day, and Sweetie quickly takes advantage as she has the butler go get some hamburgers for her.
Meanwhile, Chase's attempts to escape his cell fail as an attempt to jostle the trap door chute open with his tennis ball cannon results in the tennis balls bouncing and ricocheting all over the place.
As for the rest of the PAW Patrol, reaching the moat, Ryder has Zuma head underwater and use his new sonar and aqua drone to find Chase's bow tie and retrieve it. Rubble asks Ryder what sonar is. Ryder explains it is using sound waves to find something that one cannot find underwater. At the same time, hearing Zuma's sonar pings on the other side of one of the cell walls, Chase attempts to find some way to get their attention. After noticing one of his tennis balls bounce off the metal dog bowl in his cell, Chase fires tennis ball after tennis ball at it after planting in against the wall, hoping someone will hear. Luckily, Zuma hears it with his sonar, and Ryder takes Marshall and Rocky with him while the others return to the cruiser. Once they locate Chase's cell, and Rocky confirms Chase is inside with his radar, Ryder has Rubble bring his mini-miner down to drill into the cell and free Chase. Reunited, Chase reveals he knows who the real thief is, and the team head back up to the throne room.
Inside the throne room, Sweetie is enjoying herself, before the PAW Patrol, with Chase now in his Mission PAW suit and equipment, arrive to expose her. Using the camera footage from Chase's bow tie, they prove to the Earl and Princess that Sweetie is guilty and not Chase. The Princess is very disappointed and cross with Sweetie and demands her crown back. Busted, Sweetie attempts to escape on her personal vehicle, but Chase, Skye, and Ryder pursue her with Chase on his new three-wheel patrol vehicle, Skye on her sky-cycle, and Ryder on his skateboard. Seeing that escaping on the road won't work, Sweetie converts her vehicle to helicopter mode, but Skye does the same with her sky-cycle. As Skye chases down Sweetie, Sweetie makes the mistake of trying to evade Skye, as when she turns her vehicle inverted, the Crown of Barkingburg falls off her head, causing her to make another mistake with unbuckling herself to fall after it to retrieve it, realizing afterwards that unbuckling herself was a bad idea. However, Skye catches the crown with her Mission PAW suction cup launcher, and Chase catches Sweetie on the ground with the airbag from his three-wheel. Tired, exhausted, and surrounded, Sweetie admits defeat.
As punishment for her thievery and lying, Sweetie is confined to her doghouse, surrounded by a wrought-iron fence high enough to treat her doghouse like a jail cell. Upset with how badly her plan fell apart at the last minute, Sweetie blames Busby for what happened, only to begin to feel sympathy for him and hugs him close. As for the PAW Patrol, the Princess apologizes to Chase for doubting him, while the Earl rewards them for their heroism with a special treat made by the royal baker. As the pups dig in to their rewards, Ryder assures the Princess and Earl that if Barkingburg ever needs their help again, just yelp for it.