Our heroes return to the Driftveil City Gym and Ash once more challenges Gym Leader Clay to a battle. But once again Clay again tells them he’s too busy to accept Ash’s challenge—this time because he has run out of Revival Herbs. Clay makes a deal with Ash: if Ash can bring him some of these amazing medicinal herbs, Clay will accept his challenge. So our heroes set off to the Driftveil Market to find some.
The gang asks their friend Charles for help, to no avail. Then they learn that the only place where Revival Herbs grow is on Milos Island, known as the Island of Legends. Ash, Iris, and Cilan arrive on the island and are told to seek out a guide named Lewis. They travel a great distance to find him, but Lewis sadly tells them that he can’t find any Revival Herbs either...there hasn’t been any rain for a very long time, and all the herbs have dried up.
Lewis and his Gothorita have planned a rainmaking ceremony to appeal to the Legendary Pokémon Landorus, whose presence is said to make the land fertile. But the Legendary Pokémon Tornadus and Thundurus appear instead, and immediately start attacking each other and our heroes! Tornadus and Thundurus had been blocked from returning to Milos Island by two protective obelisks, but we discover what Team Rocket has been up to recently: tampering with the obelisks to make them stop working. Now the two powerful Legendary Pokémon are back, and they’re ready for a fight—and their rage could destroy Milos Island!
Our heroes valiantly attempt to battle Tornadus and Thundurus, but the angry Legendary Pokémon prove too powerful. Lewis remembers that Landorus is said to be the only one who can control Tornadus and Thundurus, but it can only be summoned by a Shrine Maiden. Iris assumes the identity of the Shrine Maiden, and with Gothorita’s help, begins to send her appeal to Landorus. Will she be able to make contact with the Legendary Pokémon and save Milos Island?
On Milos Island, Lewis picks a Revival Herb from the ground only to find that it is dead. He realizes there must be a major disturbance and looks up at the sky, noticing dark clouds rolling in. A bolt of lightning strikes Thundurus' obelisk. Meanwhile, Ash and his friends head back to the Driftveil Gym to challenge the Gym Leader Clay. Clay tells them that he has no time for a Gym battle and must find a Revival Herb. Ash offers to get some Revival Herb for him, and Clay promises to battle Ash if he brings Revival Herbs to him. Ash, Iris, and Cilan head to the market and find Charles there. Charles tells them that he is there to pick up Revival Herbs, but the man who usually has them informs everyone that he cannot give them any. Charles suggests that they head to Milos Island, also known as the island of legends, where Revival Herbs are known to grow.
Once they arrive on Milos Island, they meet an older woman. They ask her about finding Revival Herbs, and she says that Lewis will be able to help them. They locate Lewis in the mountains and ask him about the Revival Herbs, so he invites them inside his cabin. Everyone looks over to a bed and notices that Lilligant is really sick and bed ridden. Ash scans Lilligant with his Pokédex. Lewis mentions that like all of the Revival Herbs, the Grass Pokémon on Milos Island are also showing signs of being very sick. Lewis explains the local legend, which explains that Landorus stepped in to stop Thundurus and Tornadus from fighting, but was injured as a result. A Gothorita used Revival Herbs to help Landorus recover, and it went onto banish the duelling forces before restoring the land to a pristine environment. Lewis admits that the islands are hosting a rain making ceremony in the hopes of rejuvenating Milos Island. Soon, Lewis's Gothorita arrives inside the cabin and explains that there was no sign of any live Revival Herbs. Lewis crumbles up the dead Revival Herb in his hand, but reminds Gothorita not to be disheartened. Gothorita meets Pikachu and Axew, and it appears to really like Axew.
The following day, Lewis, Ash, Iris, and Cilan head to Landorus's obelisk. Lewis sets a fire and calls out for Landorus' help. Gothorita uses her Psychic powers to also ask Landorus for help. Suddenly a tornado-looking cloud appears and blocks Gothorita's attempt to communicate with Landorus. Tornadus breaks free from the cloud and appears. He attacks everyone with Hurricane, Air Slash and Hidden Power while Pikachu fights back with a Thunderbolt. Everyone runs away, but Cilan stays back to try to keep Tornadus from chasing after them, having Pansage use Bullet Seed on him. Lewis, Iris, and Ash head toward Tornadus' obelisk and discover that an important part, the wedge, had been destroyed. Lewis suggests that they should check Thundurus's obelisk as well. Meanwhile Pansage is really having trouble with Tornadus, and tries to use Solar Beam but Tornadus redirects it towards the others. Iris and Axew are sent flying but Gothorita saves them with Telekinesis.
Before Lewis, Iris and Ash can check on Thundurus's obelisk, a bolt of lightning strikes down on the monument. Thundurus appears out of the lightning and begins to attack with Thunder and Focus Blast. He heads towards the other island to confront Tornadus, reignited their ancient battle. Pansage is recalled after being hurt so badly from the battle with Tornadus. Tornadus and Thundurus begin fighting each other back and forth. Cilan suggests to Ash that he should try to stop them from attacking. Ash brings out Snivy and has her use Leaf Storm but Tornadus uses Hurricane to blow her back forcing her to grab onto Ash's arm with Vine Whip to land safely. Iris brings out Excadrill to battle them. Iris has Axew use Dragon Rage as well.
Meanwhile at a distance, Team Rocket is watching the whole battle take place. Team Rocket discusses how they will let the Pokémon wear themselves out and execute their plan when the time is right. Pikachu and Stunfisk try to use a combined Thunder Shock and Thunderbolt on Tornadus, but he blocks the attacks. Tornadus and Thundurus are both proving to be too strong and are damaging everyone's Pokémon. Lewis asks Gothorita to use her powers to try to communicate everyone's feelings to them, but it doesn't work and they keep attacking each other. From the disturbance, lightning sparks raging forest fires across Milos Island, and the sea becomes choppy.
Lewis tells Ash, Iris, and Cilan that they must try to summon Landorus and ask for his help. Lewis also explains to Iris that she is the only one who can ask for Landorus' help. In her shrine maiden outfit, Iris kneels down in front of Landorus' obelisk and calls out for his help. Lewis places four colored orbs around Gothorita, who uses its powers to lift the four colored orbs and increase the strength of their cries of help. A light shoots up into the sky and hits the obelisk on the way down lighting it up. Tornadus and Thundurus continue their battle, and a shadow of Landorus begins to emerge.