Cynthia appears after having watched Piplup, Turtwig, and Chimchar evolve simultaneously. Platinum, Diamond, Pearl are surprised to see her and decide to tell a joke in order to determine if she is a good person or not. Cynthia laughs at this and introduces herself to the group. The group decides that she doesn't seem like a bad person since she laughed at their joke, and then Cynthia offers to give advice for their Gym match at the Eterna Gym. As Diamond is eating a rice ball, it suddenly goes up his nose and he hurls it out of his mouth, startling Prinplup, who then fires a blast of water towards a building. Quickly, Cynthia's Spiritomb uses Psychic to stop the blast in midair, as the group watches in amazement. After a bit of training with Cynthia against her Spiritomb, the group thanks her as they leave for the Eterna Gym. Cynthia watches and has slight nostalgia while she reminiscences about having a Pokédex as she watches the group go. It is then revealed that Cynthia came to Eterna City to investigate the disappearance of Rad Rickshaw.
Meanwhile, the trio reach the Eterna Gym and Platinum takes up the challenge. However, Diamond and Pearl are not allowed to proceed further into the Gym to keep things fair, seeing as how they are not participating. The two instead climb up a tree and are surprised to see Platinum has already made it past the four hidden Trainers and is about to begin battling Gardenia, the Gym Leader. In a Double Battle, Platinum starts off her Ponyta and Prinplup against Gardenia's Roserade and Cherubi. Though Platinum has a clear type advantage, her Ponyta quickly loses against Roserade.
Elsewhere, Rad Rickshaw is tied up at the Team Galactic Eterna Building, but is quickly rescued by Cynthia along with her Spiritomb and Garchomp, though he is not aware who saves him.
Back at the Eterna Gym, Prinplup is getting pummeled by both Cherubi and Roserade. This quickly changes as Platinum takes advantage of the holes made in the ground by Grass Knot and uses that to direct Blizzard unnoticed at both Cherubi and Roserade, knocking them out cold. Platinum is then awarded the Forest Badge by Gardenia. As the trio leave the Gym, Rad Rickshaw approaches them and mistakenly credits them for saving him and then gives them each a bicycle. The next morning their bicycles arrive at the Eterna Grand Hotel.