In 1770, Italian man Cassius had been disowned by his parents for saving a whale from being hunted. While he is wallowing away by the ocean one day, a couple of mermaids call out to him, and they drag him into the ocean. Once they reach their home, the Lost City of Atlantis, they show their catch to Prince Triden. He then goes to his dying father Neptune to show the human. Neptune, to everyone's shock, greets the human warmly. Neptune then reveals that he saw Cassius save a whale. Neptune then gifts Cassius a blue stone. Cassius takes the stone, which instantly breaks, sending out a shockwave. Neptune then merges with Cassius and grants him water breathing, the power to swim super fast, and the ability to communicate with all marine creatures. Triden, now King of Atlantis, grants Cassius Neptune's trident. The movie ends with a scene a decade later in 1880, when Romanius moves to California after hearing about the California Gold Rush. He changes his River Aeneas. We see River using Neptune's powers and cut to the credits.
