Somewhere out in the ocean, Carlos and Tracker arrive on an island where they believe there is buried treasure from a legendary pirate they read about. They are soon joined by Matea, but as they start to explore, they trigger one of the pirate's booby traps, resulting in Tracker losing his pup-tag as it is lost underwater and carried away by the current, and their boat is destroyed from being impaled by the column it was raised up on. With no way to reach Ryder in Adventure Bay, Carlos decides to send Matea to contact Ryder.
In Adventure Bay, the pups and Ryder are at Adventure Beach, pretending to be pirates, when Matea arrives with Carlos and Tracker's call for help and a map to their whereabouts. Seeing that their friends need their help, Ryder summons the pups to the Sea Patrol HQ. Once there, Rubble questions on why they were still wearing their pirate hats and Ryder replies that they are on a pirate adventure. He then briefs them on the mission and assigns Skye, Rubble, and Zuma to assist with helping rescue Carlos and Tracker, and as they descend into the bridge of the Sea Patroller, Robo-Dog is sporting his own eyepatch and pirate's hat as he loads up Zuma and Rubble's Sea Patrol vehicles, and the Sea Patroller sets sail for the archipelago where Carlos and Tracker are, sporting a PAW Patrol Jolly Roger of the PAW Patrol badge and a pair of crossbones from the top of the ship.
As they head for the archipelago, the pups sing a sea shanty of their mission, before they reach the island where Carlos and Tracker are. Skye heads up on her parasail to look for them and manages to find them, but after Rubble and Zuma deploy in their vehicles, they find their path blocked when another booby trap is sprung and blocks the Sea Patroller's path with more columns that prevent further approach to the island. However, Zuma and Rubble manage to knock them down like dominoes, and the Sea Patroller is able to reach shore. Once there, they begin exploring the island until they find a treasure chest, only to open it and find nothing inside except for a golden whistle. However, when Carlos plays it, it causes all the nearby wildlife and sea life, including crabs, crocodiles, monkeys, sharks, and snakes, to become entranced, causing them to carry the chest, which Carlos was still standing in, to another island where the pirate stored his treasure with the animals as his loyal crew and guards.
Once the Sea Patroller reaches the next island, in order to pursue Carlos, who Tracker can locate with his ears, Ryder has Robo-Dog convert the Sea Patroller to amphibious mode, allowing them to travel onto the island to find Carlos. As they do, Ryder encourages Tracker to attempt to remember the counter-song on the flute to break the trance on the animals. Tracker remembers most of it, and nearly reverts the hypnosis, but can't remember the ending, but agrees to keep trying.
They soon locate Carlos where the entranced crocodiles brought him, which should be where the rest of the pirate's loot is located, but it is clear that Carlos can't get away, and the PAW Patrol can't get close, as the crocodiles, monkeys, and a snake, show how loyal they are to the late pirate while entranced, as they surround Carlos and refuse to budge. An attempt to have Chase lure them away with treats doesn't work, and only results in the monkeys returning fire with bananas. However, Chase notices the music notes engraved on the wall of the mountain, and Ryder believes those are the counter-song needed to break the trance. With Tracker agreeing to get close and play the counter-song, Tracker uses his grappling cables to reach the wall, dodging the bananas the entranced monkeys fling at him, and begins to play the counter-song, while Marshall helps keep the bananas away from him with his water cannons. Tracker nearly finishes the song, but a well-timed banana splatters over the last note, obscuring it from Tracker's view and causing him to momentarily interrupt himself with some sour notes, but Marshall manages to wash the banana off, allowing Tracker to resume and finish the song, breaking the trance on all the animals, who are initially confused when they are freed from the trance, but quickly take off to return to their normal lives, while a final hidden switch as the Sea Patroller was leaving to retrieve Tracker's Jeep opens the wall where the notes were inscribed to reveal the pirate's hidden loot, which amazes the pups, Carlos, and Ryder.
Some time later, the PAW Patrol prepare to return to Adventure Beach, after giving Tracker a new pup-tag to replace the one he lost, and after Carlos and Tracker thank the team for all their help and how they can find their own way home from here, the Sea Patroller sets sail for Adventure Bay again, as the pups sing a reprise of their sea shanty as they do.