At Cerise Laboratory, Ash and Goh watch a television interview of a captain who was saved from a shipwreck by a Dragonite. Ash says he'd love to meet a Dragonite someday, but Ren explains that, even though they're very popular, Dratini and its evolved forms are very rare in the wild. Professor Cerise mentions rumors of an island supposedly inhabited only by Dragonite, exciting Ash. Goh then shows a map displaying the Dragonite sightings from the last the few years, all of which seem to center around a certain area. Based on this information, Ash and Goh embark on a quest to find the Dragonite Island.
Traveling aboard a ship, Ash notices Goh's bag is full of Poké Balls, as he intends to catch every member of the Dratini evolutionary family. As the ship docks, Goh decides that instead of renting a boat to find the island, they should just catch one of the local Dewgong and use it as their ride instead. As they rush off to do just that, Team Rocket appears behind them, also planning to capture a Dragonite for the Boss. Having overheard Ash and Goh's goal to find Dragonite, they choose to enact their own capture plan immediately.
Goh has successfully found a Dewgong and throws a Poké Ball at it, but it pops out almost immediately. Undeterred, Goh throws another Poké Ball, with equally unsuccessful results. Now starting to lose his patience, Goh throws Ball after Ball at Dewgong. After numerous failed attempts, he succeeds in catching it and adding its data to his Pokédex. As Ash and Goh ride across the sea and try to locate the Dragonite Island, another Dewgong swims by, and Goh's Dewgong starts chasing after it, having fallen in love with it. Ash notices that Goh's lovestruck Pokémon is carrying them straight towards a storm. Goh's Dewgong soon loses sight of its crush, and the rough storm waves throw Ash and Goh off of its back. Just before passing out, Ash sees a group of Dragonite flying towards him.
Later, Ash and Goh regain consciousness on a beach, and are surprised to see themselves surrounded by Dragonite. They realize that they are on Dragonite Island, much to their excitement. Ash thanks the Dragonite for saving them, and Goh prepares to catch one of them. However, upon reaching into his bag, he's devastated to find out that it's completely empty, and realizes that he had ended up wasting all of his Poké Balls while trying to catch Dewgong, which has also now gone missing. Ash offers to give him one of his Poké Balls, but Goh tells him to keep it, as he might need it himself.
A Dragonite and a Dragonair offer to show Ash and Goh around the island, and they happily accept this rare opportunity. Traveling through the island's lush forests, they see Dragonite all over the place. Goh picks up his Rotom Phone asks it where they are, but it's unable to provide an answer, as there is no GPS coverage in the area. The group arrives on a clearing, where a trio of Dragonair are dancing together. As they glow and start flying around, Ash notices that their guide Dragonair is looking sad.
Scorbunny suddenly appears with a cover over its head. Goh recognized the cover as a shed skin of a Dratini, and asks Scorbunny to lead them where it found it. Scorbunny leads them to a cave behind a waterfall, where multiple shed Dratini skins are lying around. They also get to witness a Dratini shedding its skin before their eyes. Goh takes a picture of Ash holding a Dratini skin for research purposes. As the two sit around, Ash wonders out loud why Dratini and Dragonair evolve into something as drastically different from them as Dragonite, which has arms and legs, while they don't. Goh agrees, saying that something like a Milotic would make more sense as their evolved form.
As they ponder, their Dragonite and Dragonair guides sense something and start moving away, promoting Ash and Goh to follow them. As they walk, Goh says that he's figured out the island's secret. The Dragonair playing together earlier were releasing their powers to manipulate the weather, which they use to create a constant storm around the island to keep it hidden. Arriving at the beach, Ash and Goh see multiple Dragonite taking flight and effortlessly flying into the storm around the island. However, the Dragonair that they had been following struggles to get airborne, and is left behind as the last Dragonite leaves. Again and again, it flaps its wings, but keeps falling back down. Ash approaches Dragonair and offers to train with it. A little while into the unsuccessful training, Goh remembers something and shows Ash a video of the Dragonair trio's earlier dance. Ash realizes that they were probably using Dragon Dance. After consulting Rotom, Goh realizes that Dragon Dance was what the Dragonair had used to become airborne. Hearing this, Ash offers to teach Dragonair how to use Dragon Dance by showing an example himself, much to Goh's bafflement.
Ash has Pikachu use Electroweb on some rocks, creating a bouncing platform to practice on. As soon as Ash jumps on it, however, he is shocked and falls off. Goh protests that Electroweb can't be used as a trampoline, but Ash nevertheless tries again, and is shocked again. Still, he refuses to give up, wanting to give Dragonair a proper demonstration on flying. As he jumps in for another attempt, Dragonair joins him, and the two manage to endure the shock to bounce into the air. Ash notices Dragonair starting to glow, and tells it to spin more. During the second bounce, Dragonair successfully uses Dragon Dance and finally gains flight. Overjoyed, it happily wraps around Ash for a thankful hug. However, it suddenly senses something and prepares to take off. Ash tries to board it, but notices that its skin is too slippery. Goh then notices his Dewgong at the shore, heartbroken of having lost his crush, and Ash and Goh board it to follow after Dragonair.
Out in the sea, a disguised Team Rocket is floating on a raft, having succeeded in their plan in pretending to be shipwrecked to lure in a Dragonite for capture. Dragonair then arrives with Ash and Goh, and the trio throws off their disguises to perform their motto. They decide to catch Dragonair and Pikachu too, and call for Team Rocket's Pelipper, who drops the Rocket Prize Master down for them. They activate it, but only get one Poké Ball instead of the usual two. Nevertheless, they throw it, and out comes a Wailord. From its information leaflet, they see that it only knows Splash, but Meowth says that a Splash coming from an amazing Pokémon like that must be great. Jessie orders Wailord to use Splash, which throws both sides around. While Team Rocket is still recovering, Ash quickly has Pikachu use Iron Tail on Dragonite's cage, freeing it. In retaliation, Jessie orders another Splash, which actually ends up breaking Team Rocket's raft apart. One of the logs from the broken raft hits Wailord in the face, and it flails in pain, creating a huge splash that sends Ash flying into the air. Dragonair dives down from the sky to save him, but its slippery skin prevents Ash from grabbing a hold of it. Suddenly, Dragonair starts to glow and evolves into a Dragonite, who uses its newly developed arms to grab Ash and save him just in the nick of time. The first Dragonite then promptly flies in front of Team Rocket, its face twisted with anger, and fires a point-blank Hyper Beam to send them blasting off.
Standing on Wailord's back, as Ash and Goh watch the first Dragonite congratulate its newly evolved brethren, Ash tells Goh that he's figured out why Dragonite have arms: it's so they can protect others. The two prepare to leave, but the newly evolved Dragonite pulls Ash into a tight, friendly embrace. Ash realizes that Dragonite wants to come with him, and happily accepts its request, pulling out a Poké Ball and catching it. Ash celebrates his new capture, accompanied by Wailord making a celebratory water spout.
Back at Cerise Laboratory, Professor Cerise is impressed of Ash and Goh having proven that the Dragonite Island actually exists. However, he surprises Ren and Chrysa by saying that he's not going to publicly announce these findings, seeing that the air of mystery around the Dragonite is part of their appeal. Ash's Dragonite thanks him for this declaration with a friendly bear-hug.