Team Rocket has captured Meloetta, brought it to the Undersea Temple, and used a recording of Meloetta's song to raise the temple to the surface. As Operation Tempest continues, Giovanni acquires the mysterious Reveal Glass and uses it to summon the three Legendary Pokémon Tornadus, Thundurus, and Landorus!

Meloetta's protector, Ridley, explains that whoever controls Meloetta also controls these three ancient powers. Team Rocket’s plan is just the latest attempt by evildoers over the years to take over the Unova region using the power of the Reveal Glass. Our heroes watch in horror as the three Legendary Pokémon change into Therian Forme and prepare to wreak havoc upon Unova! As Ash and Pikachu escape from their cage, an enormous Pokémon battle takes shape: Iris's Dragonite, Cilan's Pansage, Cynthia's Garchomp, Ridley's Golurk, and Ash's Unfezant join with Pikachu to stand against the fearsome Tornadus, Thundurus, and Landorus. A crackling attack from Thundurus almost strikes Iris down, but Pikachu flings itself into the bolt's path to protect her. Using the extra electricity it absorbed from that attack, Pikachu launches a massive Electro Ball to overpower Team Rocket and free Meloetta!

But Giovanni still holds the Reveal Glass, and without Meloetta's calming influence, he is completely overcome with evil ambitions: instead of conquering the Unova region, he now wants to destroy it! But Jessie, James, and Meowth intervene to sway their Boss from this disastrous path. As soon as he returns to his senses, Team Rocket reluctantly retreats.

Ridley uses the Reveal Glass to return the three Legendary Pokémon to their Incarnate Forme, and Meloetta soothes their rage with its song. With disaster averted, Ridley and Meloetta bid our heroes farewell and prepare to return to home. But Ash knows they will meet again someday, and all eyes once again turn toward the Unova League!