Plot

Black Manta seeks revenge on Aquaman for his father's death. Wielding the Black Trident's power, he becomes a formidable foe. To defend Atlantis, Aquaman forges an alliance with his imprisoned brother. They must protect the kingdom.

Having failed to defeat Aquaman the first time, Black Manta, still driven by the need to avenge his father's death, will stop at nothing to take Aquaman down once and for all. This time Black Manta is more formidable than ever before, wielding the power of the mythic Black Trident, which unleashes an ancient and malevolent force. To defeat him, Aquaman will turn to his imprisoned brother Orm, the former King of Atlantis, to forge an unlikely alliance. Together, they must set aside their differences in order to protect their kingdom and save Aquaman's family, and the world, from irreversible destruction.—Aquaman Movie

Arthur Curry, the rightful heir to the underwater kingdom of Atlantis, grapples with parenthood and the weighty responsibilities of ruling over the Seven Seas. And then, as if that weren't enough, a long-forgotten force suddenly emerges. As dark powers ravage the oceanic world and threaten to destroy everything in their path, the new king of Atlantis is with his back to the wall. As a result, Arthur must form an uneasy alliance with an old foe and embark on a perilous journey to defend his family, the kingdom, and the entire planet from the irreversible devastation that looms on the horizon. Will Aquaman (2018) rise to the occasion and defeat the ominous menace of the lost kingdom?—Nick Riganas

Arthur Curry has married Mera and had a son, Arthur Jr., and splits his life between land, where he lives in the lighthouse of his father Tom and fights crime, and the sea, ruling as the King of Atlantis. However, Arthur finds the diplomatic and bureaucratic royal duties boring, and is always entering conflict with the Atlantean council, who are particularly opposed to Arthur's intent of making Atlantis contact the surface world. Meanwhile, David Kane continues to seek revenge against Aquaman, and follows the research of marine scientist Stephen Shin to look for Atlantean artifacts. Once in an Atlantean ruin underneath the Arctic ice, David finds a black trident, that leads him to be possessed by its creator, who promises that if David helps his Atlantean tribe recover, David will receive the power he desires to destroy Aquaman, his family, and his kingdom. Five months later, global warming has worsened, with the surface's climate experiencing extreme weather, and the ocean acidification causing diseases in the sea population. Atlantis is attacked by Black Manta, who takes the kingdom's orichalcum reserves to power his ancient Atlantean machines restored by Shin, injures Mera, and proves himself capable of fighting Arthur in equal terms. Reconvening with his mother Atlanna and Mera's father Nereus, Arthur discovers that David is behind the rising temperatures, as he went after all the hidden reserves of orichalcum, which emits high quantities of greenhouse gases and nearly caused a planetary extinction when used by an ancient Atlantean kingdom. Arthur decides that the way to find out where the Black Manta is hidden is going after one of David's allies, Arthur's half-brother Orm Marius, held captive by the Fisherman kingdom for having killed their king. Arthur breaks out Orm from prison, and after a meeting with crime lord Kingfish discovers David is based on a south Pacific volcanic island. Arriving in the island, Arthur and Orm discover monstrous fauna and flora that had been mutated by an orichalcum furnace where Black Manta's base is located. Before Atlantis attacks and destroys the island, Orm gets hold of the black trident and has visions revealing its creator was Kordax, the brother of Atlantis founder King Atlan and ruler of the lost kingdom of Necrus, that wound up sealed in an icy prison after losing a war with Atlantis. Given the seal was created by Atlan with blood magic, the blood of any of his descendants could release Kordax, leading David to attack Tom Curry's lighthouse and kidnap Arthur Jr. before heading to Necrus's hiding place, that the Atlanteans discover with Shin's help to be underneath the ice of Antarctica. In Necrus, Arthur attacks David to stop him from injuring Arthur Jr., and David almost defeats Arthur before Orm arrives and disarms him of the black trident. As Orm gets hold of the trident, the spirit of Kordax leaves David for Orm, who proceeds to fight Arthur and use his blood to thaw the ice imprisoning the body of Kordax. With his half-brother freed, Arthur throws the black trident at Kordax, who catches it in mid-air, before throwing his own trident to destroy the black trident and fatally impale Kordax. With Kordax's magic vanishing, Necrus starts to collapse, and as David hangs from a fissure, he refuses Arthur's help and throws himself down the cliff to his death. The Atlanteans and Shin escape to safety, and Arthur and Mera decide to let Orm go and tell the rest of Atlantis that he died, on the condition he remains hidden. Arthur decides that uniting land and sea is necessary to combat climate change, and reveals Atlantis to the human world through an announcement to the United Nations, with the intent of making the underwater kingdom a member state.