Following the events of Darkseid's invasion, the undersea kingdom of Atlantis is in turmoil after the mysterious death of its king. Arthur Curry, a seemingly ordinary man who feels out of place in the human world, discovers his Atlantean heritage and his connection to the throne. His half-brother Orm Marius, fueled by a thirst for power, plots to declare war on the surface dwellers, believing they are responsible for their father's death. As tension builds, Queen Atlanna, Arthur’s mother, reaches out to him in hopes that he will ascend to the throne and unite both worlds.

Meanwhile, the Justice League, consisting of heroes like Superman, Batman, Wonder Woman, Green Lantern, Flash, Shazam, and Cyborg, detect strange occurrences and potential threats from beneath the ocean. They prepare to counter any aggression but soon realize they must assist Arthur in his quest to embrace his destiny and prevent a catastrophic war. With the guidance of his mentor Vulko and new friends from the surface, Arthur must navigate political intrigue, family betrayal, and intense combat as he grows into his role as a leader and protector for both Atlantis and the surface world.