Pokémon : S5 | E11 – The Mystery Is History

Ash and his friends are pleasantly surprised to see Sparky in front of them and his Trainer, Ritchie soon approaches them. Ash asks what Ritchie is doing here. Ritchie explains that after the Indigo Plateau Conference, he heard about a mysterious Pokémon in the Whirl Islands. His extensive research has led him to Ogi Isle, and Ash recalls his own encounter with something near Blue Point Isle. Ash boasts about his natural instinct, but Brock figures that there is a reason that both they and Ritchie are on Ogi Isle. Ritchie points out a nearby island, and soon he and the group row over to it.

Meanwhile, on the island, a local boy, Oliver plays with his Lanturn and good friend Silver, who remains only a shadow silhouette underwater. He soon spots the group’s rowboat and calls for Silver to hide in the meantime. Ritchie and the others make land and introduce themselves to Oliver. Ash declares that they are looking for a mysterious Pokémon. Oliver seems nervous, almost as if he was faking his uncertainty before swimming off to avoid more questions. Ritchie is suspicious, but with no answer, the gang goes off to comb the island. When the coast is clear, something pulls Oliver under the water, his friend Silver, a young Lugia.
(Source: Bulbapedia)