Continuing their journey to Nimbasa City, Ash and friends are suddenly woken up in the middle of the night by a mysterious light. Soon after they encounter a professor and the mysterious Pokémon Elgyem.

While taking a break on their journey, Ash and friends come under attack by wild Pokémon and the gang's Pokemon are badly poisoned. The only thing nearby that can heal them are herbs found at the bottom of a nearby lake. However, when Oshawott goes to get them, it is attacked by a wild Palpitoad and Stunfisk. Now everyone must find a way to stop the two Pokémon and heal the gang's Pokemon.