Our heroes narrowly miss the ferry to Redrock Isle, but are fortunate enough to bump into a Pokémon researcher and a deep-sea diver who offers to carry them across the strait in her boat. En route they learn of a longstanding goal she is just now attempting to reach—her great-grandfather had made a valuable discovery, but been discredited when the find was lost in a shipwreck, the location of which she has only recently discovered. Excited by her tale, the young Pokémon Trainers decide to accompany her in a dive down to the ruined ship and witness as she recovers the article that will restore her great-grandfather's honor in the scientific community. Their attempts to approach the sunken ship, however, are routed by an aggressive Mantine and a number of Remoraid. In order to take up her great-grandfather's legacy, this researcher, with the help of Ash and friends, must first explain the strange defensive behavior of these Pokémon.