As they near Shalour City, Ash & Co. learn of a Pokémon Summer Camp being held by Professor Sycamore. In this camp, the trainers compete with each other in various activities, and get scored based on it with the top trainers entering the special Hall of Fame. When at the camp, they meet a trio of trainers, Shauna Trevor & Tierno who have Bulbasaur, Charmander and Squirtle as their partner Pokémon. A rivalry quickly develops between the seven and the Summer Camp begins...

The Pokémon Summer Camp competition is heating up with Ash & Tierno's teams having the exact same amount of points. The next challenge is PokéEnteering, where each team has to go to various locations and collect stamps, and the fastest time wins. Both teams go smoothly through the challenge, but soon a mysterious mist appears and Bonnie gets lost. To top it off, she sees the legendary Pokémon, Xerneas. Will Ash, Tierno & co. manage to find Bonnie and still win the competition?