While Ash and his friends make their way through a desolate land and towards Snowbelle City, Clemont is struggling in the harsh conditions. He asks where the next Pokémon Center is, but Serena says they are quite a way away from anything. Bonnie is completely unfazed by the heat. Clemont wishes he could be carried like Dedenne or Squishy before collapsing from exhaustion, causing Chespin to hold him up. Ash notices a robot scraping the soil in the distance, which gets Clemont's attention as he is overcome with excitement. Clemont is impressed by the old robot and its ability to talk. The robot orders the group out the way as it plants seeds and covers them with soil, and Clemont comes to the conclusion that someone must have programmed it to do all this work despite the dry conditions. Just then, a Seed Bomb attack is sent towards the group as a Pokémon stands on top of a rock, staring at them. Ash scans the Pokémon with his Pokédex and it is revealed to be a Chesnaught. The Spiny Armor Pokémon charges right towards them. Chespin runs forward to protect them, only to run in the opposite direction when it realizes that it stands no chance. Everyone else goes into hiding as Chesnaught continues its approach, all while a young boy watches from behind a rock. As the group hides from Chesnaught, they wonder why it would just suddenly attack them out of nowhere. Serena and Bonnie suggest that Chesnaught is trying to protect the robot. Just then, Chespin informs them of a nearby building.
Upon arriving at the building, the group notice its decaying state and find that nobody is around. Serena says that it looks like a research lab. As they look around, they notice a photograph of an old man with the Chesnaught and robot from earlier. Suddenly, the young boy from earlier calls out and asks them what they are doing. They all introduce themselves to him. The boy then asks them what they want with the Chapman Research Lab, and Clemont announces that they wanted to learn more about the robot they saw outside. The boy introduces himself as Henny and reveals that the old man in the photograph is his grandfather, Chapman. Henny shows the group a video made by Chapman, who explains what happened to the land. Long ago, the land was actually a beautiful forest inhabited by a variety of Pokémon. However, the forest began to dry up, but before Chapman could figure out the reason why, he was overcome with a certain illness. Determined to help the forest grow back, Chapman constructed a robot, Robon, to help the forest regrow.
After watching the video, Henny explains that even though Chapman is gone, Robon continues to plant seeds and Chesnaught continues to protect Robon. Just then, Robon returns to the laboratory to recharge itself, much to Clemont's amazement, but Henny explains that it takes a long time for Robon to recharge lately and thinks that it is about to break down. Clemont takes a look inside the machine charging Robon and says that it is an easy fix, but Henny says that he doesn't want Robon and Chesnaught to continue working. Clemont explains that Robon wants to replant the forest, so they should be helping Robon instead of stopping it. Henny explains that the hard work it has put in has resulted in no progress, so replanting the forest seems impossible. Clemont informs him that giving up is what will cause the progress of science to come to a stand-still, and that they need to continue on in order for them to make more progress. Everyone agrees that taking on challenges is the only way to progress and this gets through to Henny, who says he will do everything he can. Moments later, Robon is fully charged, much to Henny's surprise as he thanks Clemont for everything he did.
Back outside, everyone is ready to help Robon, but not long after, Chesnaught arrives once again to protect Robon from the group. Henny steps in to calm Chesnaught down, explaining that they only want to help Robon out, and after Chespin, Pikachu, and Clemont also step in, Chesnaught finally understands and is willing to let them help. As everyone gets ready to work, Clemont decides to check what the condition of the soil is in order to tell whether or not plants can actually grow in the area. Clemont reveals his newest machine, the Mister Dirt Analyzing Simulator, which can analyze the soil's components to determine whether plants are able to grow. After the analysis is complete, the machine announces that it is impossible for anything to grow in the soil. After wondering what to do next, Clemont realizes that if there was once a forest, then there must be underground water in the area. He sends out Luxray to use its X-ray vision to search around, as Ash sends out Noibat to use Supersonic to help out with the search. Wanting to help out, as well, Chespin uses its vines to search for water, and after seeing Clemont's praise, Chesnaught does the same and receives praise too, causing it to blush.
With everyone working hard to replant the forest, they fail to notice Team Rocket watching them from behind a nearby rock as they comment on the group being up to something weird as usual. Jessie isn't impressed and suggests that they capture the powerful looking Chesnaught, with James agreeing before Wobbuffet appears and almost blows their cover.
Continuing the search for water, Chespin suddenly finds something and alerts Chesnaught, who then searches in the same spot and hears the running water below. Chespin reports back to the group, and Noibat and Luxray search the spot themselves and confirm that there is indeed water below. After Ash, Clemont, and Henny praise the Pokémon for their work, Clemont sends out Bunnelby to use Dig on the spot, with Ash suggesting they help out. After digging for a while, Bunnelby stops because it has reached the bedrock. Unless they move the rock, they can't get to the water below. Clemont analyzes the rock and infers that seismic activity has shifted the 10 metre rock until it formed a lid. As he considers a solution, Chespin and Chesnaught try Pin Missile on the rock. While their attempt fails, Clemont thinks of a solution by heating the rock up and then cooling it down shortly after. Serena has Braixen use Flamethrower to heat the rock up, while Ash orders Greninja to use Water Shuriken to cool the heated rock down. After that, all of the Pokémon attack follow with a joint attack, but the rock fails to fracture. Clemont settles on another strategy, that they pull the rock out of the ground if breaking it didn't work.
With ropes attached to the rock, everyone and the Pokémon hold on tight and prepare to pull, but just as they start to pull, they are all captured and held together by rings. As they look up, they see that it is none other than Team Rocket, who reveal that they originally planned to capture only Pikachu and Chesnaught, but then decided to capture all the other Pokémon while they were at it. Just then, Robon arrives and orders Team Rocket to move away, as they are standing on a spot where seeds have been planted. Its request is ignored as Jessie orders her Gourgeist to attack Robon, who sends the robot flying with a Shadow Ball. This angers Chesnaught, who has its restraint tightened by Meowth, causing it to cry out in pain. Robon notices this and calls out to it as it remembers Chapman telling Chesnaught that the two should always help each other out because the two of them are the land's only hope of survival. Jessie and James have their Pokémon take care of Chesnaught as Inkay uses Psybeam and Gourgeist attacks with Shadow Ball. Though Robon jumps in the way to protect Chesnaught and takes the attacks head on, causing it to be destroyed. Chesnaught is enraged and uses pure strength to break itself out of its restraint. It uses Pin Missile against Team Rocket, which causes Meowth to drop his controller. Chesnaught steps on the controller, breaking it and setting everyone else free from the Team Rocket Trio's traps. To end this catastrophe, Ash orders Greninja and Pikachu to combine a Water Shuriken and Thunderbolt attack, Serena orders Braixen to use Fire Blast, Clemont orders Chespin and Luxray to use Pin Missile and Swift while Chesnaught uses another Pin Missile, forming a "Magna Pulse" attack to ultimately blast off them, Inkay and Gourgeist for good.
Afterwards, Henny cries over the destroyed Robon. Clemont offers some comfort to Henny by repeating his statement that the progress of science stops the moment a person gives up. Back inside the building, everyone watches in anticipation as Clemont works on repairing Robon. After a while, Clemont announces that Robon is as good as new, and the robot affirms this with a reboot status. The group goes back outside, where Clemont asks Robon what to do about the large rock. Robon scans the rock and activates its in-built drill to break through the obstacle with ease. Water immediately spouts from the ground and begins filling the dried river bed. Afterwards, Clemont once again uses his Mister Dirt Analyzing Simulator, which reveals that growth in this soil is very possible, causing everyone to cheer. As everyone watches the gusher of water, Henny is amazed at how his grandfather's dream can finally come true. Clemont reveals that as he was fixing Robon, he realized that Chapman constructed each part with incredible precision and skill. As Clemont declares that he wants to become a great inventor like Chapman, Henny announces that he wants to become a scientist, as well, and that if Robon ever needs fixing again, he'll be able to do it. Clemont expresses his confidence in Henny's ambitions, and they shake hands. Chespin and Chesnaught shake hands as well. As the sun sets, Ash and his friends bid farewell to Henny, Chesnaught, and Robon before they continue towards Snowbelle City.
Afterwards, a single budding plant in the soil is shown. Robon takes out a watering can and waters the plant, causing a rainbow to appear over the plant.