A simple kid's superhero movie with a happy ending.

Four years after "Aquaman (2018)", Arthur Curry (aka Aquaman) (Jason Momoa) is now married to Mera (Amber Heard) and they have a baby son. He enjoys his life as a family man, but hates being ruler of Atlantis.

Black Manta (aka David Kane) (Yahya Abdul-Mateen II) is out for revenge and finds the Black Trident of King Kordax (Pilou Asbæk) of the Lost Kingdom of Necrus. He is possessed through the trident, and the frozen Kordax promises him all the power he needs to defeat Aquaman if he releases him from the powerful spell that his brother King Atlan used to seal him in ice. Black Manta needs royal blood from Atlan's descendants to do this, so Arthur's baby is kidnapped.

Meanwhile the use of orichalcum by Black Manta leads to an environmental disaster. Orichalcum is a substance that is used as a power source and that releases heavy amounts of greenhouse gasses into the atmosphere, causing the temperature to rise, followed by the melting of the ice caps of Antartica.

Arthur reconciles with his imprisoned half-brother Orm Marius (Patrick Wilson) and together they commence the final battle against Black Manta. Mera rescues her baby, but is attacked by Black Manta, who throws the Black Trident at her, which is blocked by Orm. The evil Kordax then possesses Orm and he attacks Arthur, who is wounded. His blood breaks the seal and Kordax is released. Arthur succeeds in freeing Orm from Kordax' possession, and they confront Kordax before he can re-establish his evil kingdom.

Kordax is destoyed by Arthur with the Black Trident, and once again Black Manta is on the brink of death. He is hanging off a cliff and although Arthur offers to rescue him, he refuses to accept this and falls into a bottomless pit.

Arthur thanks Orm for his help and lets him go free to explore the world and its food (cheese burger ).

Finally, Arthur reveals himself and Atlantis to the Surface World (United Nations) in the hope that together they can find ways to repair the environmental damage caused by the use of orichalcum.