Our heroes are staying at Cynthia’s house while they prepare for the Pokémon World Tournament Junior Cup. After Ash and Dawn have a practice battle that ends in a draw, a worried young neighbor named Chris comes by, looking for his lost Cubchoo. The boy tells them Cubchoo somehow got out of its Pokémon house overnight, although there’s only one door and Chris is sure he locked it from the outside.
So...who will come to the rescue? Why, Connoisseur Detective Cilan, of course! After much questioning of the details surrounding the “case,” Cilan finds a small tunnel under the wall surrounding the Pokémon house, leading out to the forest. Our heroes investigate and find a surprisingly tame Beartic eating Berries nearby. Cilan decides it must have taken Cubchoo, but Dawn points out that Beartic is far too big to fit through the tunnel. Then he announces that Beartic is the missing Cubchoo, and that it must have evolved after it escaped! But when Beartic won’t return to Chris’s Poké Ball, it becomes clear that Cilan is wrong again.
Finally, they spot Cubchoo when it comes running by, playing with a wild Larvitar! The two Pokémon are obviously good friends, and Cilan deduces that Larvitar must have figured out how to open the door to Cubchoo’s Pokémon house so they could play together. He declares the mystery solved, and Ash wants to celebrate with a battle! Chris and Cubchoo have never battled before, so Ash and Scraggy battle against Larvitar to show them how it’s done. The battle ends in a draw, but Chris and Cubchoo are excited about learning to battle too! Ash and Iris suggest that the two of them set off on a journey together, and Chris says they will—as long as Larvitar comes with them.
Meanwhile, Team Rocket appears to be getting closer and closer to its mysterious target...