Giratina is the only Pokémon living in the mysterious Reverse World. Enraged when Palkia and Dialga disrupt time and space, it drags Dialga into this realm for a battle—but the conflict is broken up by Shaymin, the tiny Mythical Gratidude Pokémon. Exhausted, Shaymin leaves the Reverse World and asks Ash and his friends for help on its journey. Our heroes agree and enter the Reverse World, where they meet researcher Newton Graceland. His former assistant, Zero, seeks to harness Giratina's power to rule the Reverse World, even if that means destroying the real world! Can our heroes thwart his plans and protect both worlds? Will Giratina resolve its differences with Dialga? And what will Ash and his friends learn about Shaymin?