Born to a human father and the queen of the underwater city of Atlantis, Arthur Curry is the rightful heir to the Atlantean throne, though he remains largely ignorant of his origins, living on the surface world and using his aquatic abilities to perform heroic acts. His half-brother, King Orm, rules Atlantis with an iron fist and seeks to rally the undersea kingdoms to wage war against the surface dwellers as retaliation for the pollution and destruction caused to the oceans. Arthur is approached by the fiery Princess Mera, who seeks his help to prevent the impending war, urging him to embrace his destiny as king and to bring peace to the two worlds.

Arthur embarks on a journey to claim his birthright, which involves locating the mythical Trident of Atlan, a powerful artifact that can only be wielded by the true king of Atlantis. With the guidance of his mentor, Vulko, Arthur faces a series of challenges that test his resolve and highlight his conflicting identity as someone caught between land and sea. Meanwhile, Orm forms alliances with other underwater nations, showcasing his own might and determination to eradicate the perceived threat of humankind. The tension between the desire for power and the need for unity becomes a central theme as Arthur struggles to reconcile his responsibilities and his upbringing, setting the stage for an epic clash that will determine the fate of both worlds.