As Diamond, Pearl, and Platinum continue to Mt. Coronet, the three decide to stop at the Pokémon Mansion after Platinum mistakes it for a hotel. The owner of the mansion, Mr. Backlot, gives them all a tour of the house and the Trophy Garden. While Platinum is treated kindly by Mr. Backlot's staff, and even given a Soothe Bell, Diamond and Pearl find themselves unwelcome. They decide to let Platinum go off on her own to explore the garden, and lend her Chimler and Tru to provide her protection.
Diamond and Pearl head back inside the building to practice their routine. They are surprised to find Mr. Backlot speaking with Cynthia. Cynthia is happy to see the two, and is impressed to look through the window to find Platinum walking with the fully-evolved versions of the Pokémon she had seen the trio train with. When the boys ask Cynthia why she is visiting the mansion, she explains that Mr. Backlot has requested her help in clearing up the swarm of Psyduck on Route 210 so that people can visit Amity Square. Platinum arrives just in time to hear Cynthia's plan, and volunteers to help.
Cynthia sets the three on her Garchomp as she hops on a bicycle alongside them. To Diamond's shock, she says she wants to race Garchomp to Route 210. After they dash to their destination, Diamond is wheezing and disoriented while Pearl easily gets to his feet. From her bicycle, Cynthia removes a container with an attached hose. She informs the others that the container is filled with a Secret Potion. Telling the Psyduck to open their mouths, Cynthia uses the hose to spray the medicine over them. The swarm of Psyduck slowly clears the road, and Cynthia spots a Psyduck among them that had gone missing from a Trainer. She realizes that the congestion of Psyduck must have been caused by a person.
Now that the road is unblocked, Cynthia points out Café Cabin nearby. She walks over to it, thinking of her grandmother who loves the Moomoo Milk that is sold there. Right as she steps onto the porch, an old woman calls out to her, and Cynthia is shocked to see her grandmother right in front of her. Cynthia’s grandmother asks the four if they would like to hear the legend of the Sinnoh lakes.
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