In 1985 Maine, lighthouse keeper Thomas Curry rescues Atlanna, the princess of the underwater nation of Atlantis, during a storm. They eventually fall in love and have a son named Arthur, who is born with the power to communicate with marine lifeforms.
Atlanna is forced to abandon her family and return to Atlantis, entrusting to her loyal advisor Nuidis Vulko the mission of training Arthur. Under Vulko's guidance, Arthur becomes a skilled warrior but is rejected by the Atlanteans for being a half-breed and ultimately leaves Atlantis behind.