Ash and friends are on their way to the town where Dawn's next contest will be held. They arrive at Mt. Coronet, the massive mountain that divides the Sinnoh region in half. The mountain also divides the region's pokémon, like Shellos. The Blue and Pink Shellos have ended up on the opposite side of the mountain, and while trying to figure out why, Piplup falls into an artificial tunnel, and when they go to rescue him, they come across something sinister.

Ash and friends go to Dawn's hometown of Twinleaf. Upon arrival, they find that they made it in time for the Twinleaf Town Festival, where a Pokémon Contest is about to be held. Dawn decides to enter, and it isn't long before she finds herself facing none other than her mother, Johanna, in battle. Knowing that Johanna won the Grand Festival in the past, will Dawn be able to defeat her?