Aquaman

In 1985 Maine, lighthouse keeper Thomas Curry rescues Atlanna, queen of the underwater kingdom of Atlantis, during a storm. They fall in love and have a son named Arthur, who has the power to communicate with sea creatures.

When Atlantean soldiers sent by King Orvax (the ruler of Atlantis) arrive for Atlanna, who fled her arranged marriage, she is forced to leave her family to protect them from her people. She promises to return when it's safe and goes back to Atlantis, entrusting her advisor, Nuidis Vulko, to train Arthur. Becoming a skilled warrior, Arthur rejects Atlantis upon learning that Atlanna was executed by Orvax for loving a human and Arthur's illegitimate birth.

In the present, Arthur has become known as the metahuman dubbed as the "Aquaman" by the public. One year after Steppenwolf's defeat,[a] Arthur confronts a gang of pirates hijacking a Russian Akula-class submarine. Their leader, Jesse Kane, is killed, leading his son David to vow revenge against Arthur, after he refused to help save Jesse in retaliation for murdering innocent people.

King Orm Marius, Orvax's son and Arthur's younger half-brother as well as Atlantis's new ruler, convinces King Nereus of Xebel to help unite Atlantis and destroy the surface world for polluting the oceans. If Orm unites all four kingdoms, he will receive the title of Ocean Master, commander of the most powerful force on Earth. They are ambushed by a submarine, causing Orm to feel obligated to send a tsunami.

Nereus' daughter Mera, betrothed to Orm, refuses to aid them and requests Arthur's help. Arthur accompanies her to Atlantis after Orm's tsunami nearly kills his father. Vulko urges him to find the Trident of Atlan, a powerful artifact of Atlantis' first ruler, to reclaim his rightful place as king

Mera and Arthur are ambushed by Orm's men, and he is captured. Orm blames him for Atlanna's death and nearly kills him in a duel before Mera rescues him. She and Arthur journey to the fallen Kingdom of the Deserters hidden under the Sahara, where the trident was forged, and unlock a holographic message that leads them to Sicily, where they retrieve the trident's coordinates.

Orm gives David an Atlantean battlesuit to kill Arthur, imprisons Vulko, and coerces the Kingdom of the Fishermen to pledge their allegiance to him by killing their king. It is revealed that Orm hired David and Jesse to hijack the submarine to win Nereus's support

Rechristening himself as "Black Manta", David battles Arthur, but is defeated. Arthur and Mera fend off amphibious monsters of the Trench, and a wormhole transports them to an uncharted sea at the center of the Earth. They are reunited with Atlanna, who managed to survive and escape into the uncharted sea but was unable to find her way back.

Arthur faces the Karathen, a mythical sea monster and guardian of the trident, reclaiming the trident, which grants him control over the seven seas. Orm leads his army against the Kingdom of the Brine to declare himself Ocean Master, while in turn, Arthur leads an army of marine creatures against him.

Orm's followers embrace Arthur as the true king upon learning that he wields Atlan's trident. Arthur spares Orm's life after beating him in a duel, and Orm accepts his imprisonment after discovering that Arthur rescued their mother. Atlanna reunites with Thomas, while Arthur ascends to the throne.

In a mid-credits scene, Manta is saved by Dr. Stephen Shin, a marine scientist and conspiracy theorist obsessed with Atlantis, and agrees to lead Shin there in exchange for help in his revenge on Arthur.