During a training match against Ash’s Grovyle, Brock’s Mudkip evolves into Marshtomp and with its new power injures a nearby Flaaffy. They offer to help Flaaffy, but it turns out the girl, Mariah, has a Grandma that owns a pharmacy nearby. At the pharmacy, Flaaffy is healed. Ash and the others then learn that Grandma Katie has a student named McCauley that is learning the secrets behind medicine. Meanwhile, Team Rocket decides to steal all of Katie’s medicine.