Following the Isshu League Higaki Tournament, Satoshi and friends set out on a new journey towards the 'White Ruins' discovered by Professor Araragi's father, a place connected to Reshiram, a Pokémon called legendary. There, they meet the mysterious youth N, who claims he can understand what Pokémon are saying. And then the group gets involved in an ominous experiment on Pokémon conducted by the Plasma Gang! Through the works of the mysterious scientist Achroma, even Pikachu and Kibago become hostile towards Satoshi and friends!? What are the true ambitions of the Plasma Gang's leader Ghetsis, who reveals the gang has been searching for N!? And then, the Rocket Gang trio makes their return to the Isshu Region!! Their current mission puts them at odds with the Plasma Gang... how will the resulting battle turn out!?

(Source: Official press release; translation from PocketMonsters.net)