In 1985 Maine, lighthouse keeper Thomas Curry rescues Atlanna, the queen 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 advisor, Nuidis Vulko, the mission of training Arthur. Under Vulko's guidance, Arthur becomes a skilled warrior but rejects Atlantis upon learning that Atlanna was executed for having a half-breed son.

In the present, one year after Steppenwolf's invasion,[N 1] Arthur confronts a group of pirates attempting to hijack a Russian Naval nuclear submarine. Their leader, Jesse Kane, dies during the confrontation while his son, David, vows revenge. David later targets Atlantis at the behest of Orm, Arthur's younger half-brother and Atlantis' incumbent monarch who uses the attack as a pretext to declare war on the surface world. King Nereus of Xebel swears allegiance to Orm's cause, but his daughter Mera, who has been betrothed to Orm, refuses to aid them and journeys to the surface to ask Arthur for help, earning his trust by saving Thomas from a tsunami sent by Orm. Arthur reluctantly accompanies Mera to a rendezvous with Vulko, who urges Arthur to find the Trident of Atlan, a magic artifact that once belonged to Atlantis' first ruler, in order to reclaim his rightful place as king. They are ambushed by Orm's men and Mera and Vulko escape without having been seen, while Arthur is captured.

Arthur is chained and presented before Orm, who blames Arthur and the surface for Atlanna's death. He offers Arthur an opportunity to leave forever, but Arthur instead challenges him to a duel in a ring of underwater lava. Orm gains the upper hand and nearly kills Arthur before Mera rescues him. Together, Arthur and Mera journey to the Sahara desert where the trident was forged and unlock a holographic message that leads them to Sicily, Italy, where they retrieve the trident's coordinates. Meanwhile, Orm provides David with a prototype Atlantean battle suit to kill Arthur, imprisons Vulko after revealing knowledge of his betrayal, and coerces the remaining kingdoms of Atlantis to pledge their allegiance to him and his campaign against the surface.

After modifying Orm's technology, a fully armored David rechristens himself as Black Manta and ambushes Arthur and Mera in Sicily, grievously injuring Arthur before being thrown off a cliff to his apparent death. Mera nurses Arthur's wounds as they journey to the trident's whereabouts, and encourages him to embrace his destiny as a hero. Arriving at their destination, Arthur and Mera are attacked by the amphibious monsters called the Trench, but manage to fend them off and reach a wormhole that transports them to an uncharted sea located at the center of the Earth. There, they are unexpectedly reunited with Atlanna, who was sacrificed to the Trench for her crimes but managed to escape and reach the uncharted sea, where she has been stranded ever since.

Arthur faces Karathen, a mythical leviathan and keeper of the trident, and voices his determination to protect both Atlantis and the surface, proving his worth and reclaiming the trident, which grants him control over the seven seas. Orm and his allies lead an army against the crustacean forces of the Kingdom of the Brine with the intent of completing Orm's surface battle preparations. As Orm declares himself Ocean Master, Arthur, and Mera, with the assistance of Karathen and the Trench, intervene and lead an army of marine creatures in a battle against him. Orm's followers renounce their obedience to him and embrace Arthur as the true king upon learning he wields the trident. Arthur defeats Orm in combat but chooses to spare his life and Orm accepts his fate after discovering Arthur has found and rescued Atlanna. Atlanna returns to the surface to reunite with Thomas while Arthur ascends to the throne with Mera by his side.

In a mid-credits scene, David is rescued by Dr. Stephen Shin, a scientist and conspiracy theorist obsessed with the Atlanteans, and agrees to lead Shin there in exchange for his help in his revenge on Arthur.

https://en.wikipedia.org/wiki/Aquaman_(film)
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