Ash and his friends find a tree full of delicious honey, the scent of which has attracted several Pokémon, including Ash's Aipom and a wild Burmy. The Burmy has also attracted the attention of a Trainer, Cheryl, who captures it with her Chansey. Cheryl is a treasure hunter in search of the Enchanted Honey that's said to lie within the Amber Castle. But to find it, she needs a male Burmy she can evolve into Mothim, which has an amazing sense of smell.
Ash offers to help evolve Burmy by letting it battle Turtwig. It should be easy for Burmy to beat a Grass-type, but this Burmy isn't very robust! It loses the match and gets seized by Team Rocket as part of a nefarious plot to evolve it into Mothim and impress Giovanni. After Team Rocket makes their getaway with Burmy, however, they discover that Burmy's better at eating all their food than it is at battling.
Just in time, Cheryl and our heroes arrive to rescue Burmy. Burmy manages to help rescue itself by teaming up with Chansey to defeat Meowth and Wobbuffet, and it finally evolves into Mothim! The stage is set for everyone to join forces and send Team Rocket blasting off. That's not all—Mothim then picks up a scent and leads Ash and the gang towards a new chapter in the search for the Amber Castle!