Laki and his Smeargle are in the midst of filming an episode of their show in Melemele Meadow. Suddenly, an Ultra Wormhole appears with a mysterious creature falling through before flying off into the distance, much to everyone's surprise. Meanwhile, at the Pokémon School, Professor Kukui shows the class the result of environmental differences between an Alolan Vulpix and a Kantonian Vulpix. However, the lesson is interrupted by Komala who furiously hits the school's bell before Principal Oak enters the room. He explains to the classmates, whom he refers to as the Ultra Guardians, that Lusamine called to alert him to a new emergency, another Ultra Beast has arrived. With that, Kukui lifts the blackboard up to reveal a secret control panel. Slamming his hand to the center, he causes the book shelf and ladder to move, revealing a secret elevator shaft. Samson adds that the Pokémon School and Aether Foundation have agreed to collaborate. Kukui commands the students to get into their positions, and with that the group assemble, with a port for each of them and a larger seventh slot for their Pokémon. On their descent, Lillie explains that the elevator is just the kind of technology her mother (who she calls childish) enjoys having. Next, everyone is automatically suited up into new tight-fitting armored outfits, complete with gloves, while their Pokémon all receive special badges.
Once they arrive at the Ultra Guardians base, the group are greeted by Lusamine's Clefable, who points up at a screen. Lusamine welcomes the group alongside Professor Burnet and Wicke, and adds that Clefable is also an Ultra Guardian member and will remain at the base. She shows the footage of Laki's earlier filming, while Rotom Pokédex pull out its blond wig to cosplay as Laki. Burnet reminds Rotom to pay attention to the footage as the group sees an Ultra Beast emerge from an Ultra Wormhole. The footage shows, what Wicke has dubbed as Buzzwole, take on several Fighting-type Pokémon. The group are in awe of its power and muscular physique, and at Lusamine's digression, Rotom adds all of the Aether Foundation's data to its system. Lusamine explains that Ultra Beasts are also now considered Pokémon while Wicke notes that Buzzwole's appearance in Melemele Meadow was accidental. Lusamine adds that the Aether Foundation believe its destructive power is a symptom of it being stressed in a foreign environment, and requires that the group capture Buzzwole to protect Alola. Clefable presents Ash with a box of Beast Balls, Poké Balls specifically designed to catch Ultra Beasts, and gives Lillie a first-aid kit full of Full Restores, Max Potions, Pecha Berries, and Sitrus Berries.
Lusamine is confident the group will be fine since they faced have Nihilego before. Just as she sends them off, Lusamine has the group practice their "Ultroger" sign-offs, much to Lillie's embarrassment. They are then sent back up the elevator to select their Ride Pokémon: Ash with Garchomp, Sophocles picks Metang, Mallow pairs with Flygon, Lana soars on Dragonair, Lillie takes Altaria and Kiawe is surprised to see his Charizard. The river close to the Pokémon School opens, as the Ultra Guardians are launched in air with their Ride Pokémon. Lana and Lillie enjoy the view of the sky, while Ash believes they look cool right now.
Buzzwole lands near a lake and notices its reflection, where it flexes its muscles. Suddenly, Bewear confronts Buzzwole before the two engage in an intense match of strengths. Meanwhile, Meowth and Wobbuffet are busy harvesting berries, though stop after wondering where Bewear ran off to. They soon stumble upon Bewear fighting against Buzzwole. Meowth notes Bewear is faced with some stiff competition and is unable to translate Buzzwole’s speech. Jessie and Mimikyu stumble upon the duo, though Meowth warns her to keep quiet. Suddenly, James with Mareanie on his shoulder enters the scene, though before he can utter a sentence, Bewear grabs them all and runs.
Meanwhile, the purple creature is floating through the forest, and looks up to the sky to see the Ultra Guardians flying overhead. Ash receives a report, as Lusamine details that Buzzwole is currently fighting a Snorlax, and orders them to fly to Mahalo Trail. Rotom leads the Ultra Guardians to the task's location, just as Buzzwole has finished draining energy from Snorlax's body. Ash runs passed the casualty, though everyone else helps to heal Snorlax with a Full Restore and several berries.
Ash catches up to Buzzwole, though is perplexed to see the Pokémon busy flexing its muscles, with Rotom calling for Ash to pay attention. Pikachu starts off with a Quick Attack, though it evades and sends Pikachu into a tree. Not satisfied, Pikachu is punched into the air, passing Poipole on its ascent, and falling to the ground at a meteoric speed. Pikachu evades Buzzwole's grasp with Quick Attack and launches a strong Thunderbolt, which attracts Poipole; who is seen spinning around in enjoyment. Buzzwole sends Pikachu into a tree again, and Kiawe arrives on the scene. As he is about to send out a Pokémon, Buzzwole rushes up and inspects Kiawe before jumping backwards and again flexing. Initially confused, Kiawe flexes, to which Buzzwole continues to flex. Seeing the technique to be effective, Ash and Pikachu join in, leaving the other Ultra Guardians scratching their heads. Rotom reminds Ash to throw the Beast Ball while Buzzwole is distracted. Throwing the Beast Ball at it, the Pokémon enters rather easily, and everyone surrounds the rattling Beast Ball, only for it to stop, indicating a successful capture. As this is happening, Poipole flies up to Pikachu before knocking him over and flying off.
At Melemele Meadow, the Ultra Guardians meet up with Kukui, Lusamine, Burnet and Wicke. Burnet prepares to re-open the Ultra Wormhole with her machinery, noting it is easier to open one where it has opened before. With the Wormhole now opened, Ash calls on Buzzwole. Kukui is impressed by its size, while Lusamine tells Buzzwole that it can return home now. The Ultra Guardians send off the Pokémon with their own flexing, as it flies through the Ultra Wormhole. And with that, the Ultra Wormhole closes over. Lusamine commends the Ultra Guardians efforts and announces that their first mission was a success, to which they cheer, "Ultroger!"