Pokémon : S5 | E5 – Mantine Overboard!

Ash and his friends dash through Ogi City to make it to their next ferry, but it's too late and the vessel has already left port. Misty asks a local sailor when the next ferry will come, and he reveals the ferry to Red Rock Isle only comes once a day. Luka walks over to the group, and notices them sulking. Brock is instantly cheered up, but Misty drags him away by the ear before he scares Luka off. Luka offers to give the group a lift to Red Rock Isle in her boat, much to Ash's surprise. Brock is overwhelmingly grateful and grabs a hold of Luka's hands. Team Rocket spies from their Magikarp submarine, and they watch as Luka escorts the group onto her boat.

They soon leave port. On the deck, Ash and his friends inspect Luka's dive gear. Ash notices several pictures near the ship’s wheel and asks Luka about them. A picture of a map with a noticeable X on captivates the group's attention, and to their surprise it is a treasure map. Luka clarifies she came across the map in a journal while looking through her great-grandfather old stuff. The journal spoke of the legendary Silver Wing, a treasure said to have a link to a mysterious Pokémon. Ash recounts the group’s past encounter with their own mysterious Pokémon, but the vague details offer Luka little to go on. Luka continues her story and reveals that her great-grandfather's ship, the I.S.S Raspberry, was caught in a horrible storm and the Silver Wing went down with it. She hopes to finally prove her great-grandfather's story and has since run through some calculations to determine where the shipwreck may be lying. The potential of future instantly excites the boys. Luka likes their enthusiasm and allows them to join her. Team Rocket overhears the news and are instantly intrigued. James is keen to dive down and retrieve it, but Jessie shakes her head. Meowth is on the same wavelength as Jessie, so the trio agree to wait for the group to recover the sunken treasure for them. Jessie adds that they will steal the treasure and Pikachu as well.
(Source: Bulbapedia)