While training for the Junior Cup, Dawn arrives and mentions that Jervis told her about a nearby island that is inhabited by Onix, including a special Onix that no one has seen. Intrigued by this, everyone sets out for the island. However, things quickly take a turn for the worse when the group is attacked by the Onix on the island and Dawn and Iris become separated from Ash and Cilan. Now they must escape the attacks from the Rock Snake Pokémon and reunite so they can leave the island.