Mayor Goodway, Chickaletta, and the other residents of Adventure Bay are on the pier at Adventure Beach, waiting for the Sea Patrol to return with the Ferris Wheel of which was taken out for some maintenance and polishing. When the Sea Patroller arrives with the ferris wheel, Ryder and the pups prepare to put it back onto its anchorage. However, a mishap from Marshall makes has the ferris wheel roll away. With quick thinking, Ryder has Robo-Dog convert the Sea Patroller to Amphibious mode and they stop it in the nick of time.
Out at sea, Sid Swashbuckle and Arrby are watching everything from their ship, and chancing upon the Sea Patroller, they both decide on taking it. Arrby, concerned, then questions on how they would be able to distract the Sea Patrol away from it and Sid comes up with an idea.
Later that night, with Adventure Beach closed and everyone back home asleep, Sid and Arrby manage to wrench the end of the pier, along with the Ferris Wheel, free of its support pylons, and sail out to sea to sink it. Thus, when the Sea Patrol go to retrieve it from underwater, Sid and Arrby can commandeer the Sea Patroller once the Sea Patrol are all off-board.
The next morning, when Mayor Goodway arrives to open the ferris wheel, she finds mangled railings and support pylons where the end of the pier used to be. Realising that the ferris wheel was gone along with the edge, she immediately calls Ryder. Marshall is in better spirits as he and Zuma are on lifeguard duty at Adventure Beach, but after making another joke to get a laugh out of the other pups when Ryder summons them to the Beach Tower HQ following him crashing into them after being blinded by a life ring, they arrive to learn of what's happened. Ryder assigns Chase and Skye to aid in locating the Ferris Wheel, while Zuma is assigned to remain at Adventure Beach to keep everyone away from the damaged pier. Robo-Dog loads Chase's boat and Skye's seaplane into the Sea Patroller, and the ship heads out to begin the hunt. With clues left behind, Ryder begins to suspect that Sid is the culprit behind what's happened.
Out at sea, Sid and Arrby sink the Ferris Wheel and disconnect the mooring rope attaching the severed pier to their ship. With time in their hands, they convert their ship into submarine mode and dive out of sight before the Sea Patrol find the pier. While Skye lands back onto the Sea Patroller to help Ryder, Rubble, and Rocky in the Sub Patroller, Marshall heads out in his fire boat to aid Chase in his police boat. With Ryder requesting Robo-Dog to head down to the lower deck of the Sea Patroller to standby in case they need more equipment, it leaves the bridge unattended with everyone gone to attend to their duties.
Upon realizing that no one was on the bridge, Sid and Arrby seize the opportunity to re-surface and swing aboard. Though Robo-Dog discovers them and tries to raise the alarm, Sid and Arrby lock him below deck before managing to start the engines and successfully sailing the Sea Patroller away.
When Ryder learns of this, he has Marshall and Chase pursue the Sea Patroller, just as he had inflated the pontoons to lift the Ferris Wheel back to the surface. As Marshall and Chase pursue their shanghaied ship with their patrol boats with their lights blazing and sirens blaring, Marshall suffers another mishap with his fire boat and causes him to knock the pontoons loose, making the Ferris Wheel sink again due to his clumsiness. Despite the setback, he and Chase continue their pursuit for Sid and Arrby, only to lose them as Sid had taken the Sea Patroller ashore on to the island, hidden from plain sight.
By the time Marshall and Chase circle around to the other side of the island, there's no sign of Sid, Arrby, or the Sea Patroller. As they attempt to search again, Marshall slips on his gear shift and runs his fire boat backwards and aground on to the island where Sid was hiding. Seizing the chance to add Marshall's boat to his collection, Sid reveals himself, grabs Marshall's fire boat with the Sea Patroller's crane, and stows it below deck after swinging Marshall off. Marshall gets aboard, but is quickly conscripted by Arrby as their new crewmate, and is asked to start swabbing the deck. Marshall then hears Robo-Dog's barks for help and demands Sid to tell him where it was. Sid refuses to tell him and chances upon Marshall's shiny Pup Tag. Without any hesitation, Sid snatches Marshall's Pup Tag to keep in his new treasure chest. With Arrby telling Sid that they should get going before the Sea Patrol come looking for Marshall, they get off the island and start sailing towards Adventure Bay.
Back with Ryder and the other pups, they are unable to reach either Robo-Dog or Marshall, and fear the worst. Meanwhile, Sid comes out with a new plan where he would take the Sea Patroller back on to Adventure Beach to loot Adventure Bay, starting with the beach, including the pups' remaining Sea Patrol vehicles still stationed at the Beach Tower HQ. As he reveals his plan, he and Arrby get a good laugh or two from Marshall due to his clumsiness as he tries to get to work as their new swabbie. When they are not looking, he manages to open the chest and activate his Pup Tag to warn Ryder and the other pups of Sid's intentions, before cutting off communication to prevent Arrby from catching him. Knowing what Sid is planning next, Ryder and the pups head out for Seal Island to set up a trap for Sid with Cap'n Turbot's assistance.
Meanwhile, Sid starts his looting rampage on Adventure Beach, forcing Zuma to have everyone evacuate before their stuff can be taken by Sid. Marshall then contacts Ryder on the situation via his Pup Tag again, and is reassured that the situation is under control. He also briefs Marshall on tricking Sid and freeing Robo-Dog. As Sid and Arrby drive towards the Beach Tower HQ, Marshall manages to free Robo-Dog from the lower deck, and has it remain in cover until an opportunity to retake the bridge from Sid is prominent. As Sid closes in on the Beach Tower HQ to steal the Sea Patrol vehicles still stationed there, Ryder springs his trap, where a cutout of a pirate sloop is being illuminated into the dense fog by Cap'n Turbot using the Seal Island Lighthouse's beacon to make it seem as if there was a large pirate sloop in the distance. Chase also uses his megaphone to imitate "pirates" on-board in distress with Cap'n Turbot's help. Unable to pass up the larger opportunity, Sid abandons his plan to take the Sea Patrol vehicles and heads back out to sea.
While Sid and Arrby move towards the sloop, Marshall enters the deck and uses his clumsiness intentionally to get Sid and Arrby to chase him around, giving Robo-Dog an opportunity to retake the bridge. Once Robo-Dog is back in control of the Sea Patroller, Ryder launches the Sub Patroller onto the deck to confront Sid. Having been tricked and lost the Sea Patroller back to the Sea Patrol, Sid and Arrby prepare to flee to their "new" ship, before the ruse is dropped, forcing them to drop into a rowboat to head back to their own ship in defeat.
With the Sea Patroller back in the PAW Patrol's hands, the Ferris Wheel is finally returned to Adventure Beach, and Marshall is given special thanks for his part in helping complete the mission even though he was clumsy. Marshall then suffers one more act of clumsiness as he falls off the Sea Patroller, but lands safely in one of the Ferris Wheel seats, leaving everyone with a good laugh.