"Throne of Atlantis" is the 6th movie in the second level of The DC Movie Universe.
Trevor Donovan as King Orin/Arthur Curry/Aquaman and Thanatos
Felicia Day as Queen Mera
Donald Sutherland as Nuidis Vulko
Michael Rowe as Prince Orm Marius/Ocean-Master
Russell Crowe as Tom Curry
Teri Hatcher as Atlanna
Don Cheadle as Cal Durham
Logan Lerman as Garth
Emma Roberts as Tula
Cary Elwes as Atlan
Keith David as Black Manta
Bryan Cranston as Lex Luthor
Eliza Dushku as Mercy Graves
In the city of Atlantis, Aquaman returns after the Amazo invasion and is greeted by his new queen, Mera, Vulko, his half-brother, Prince Orm, Cal Durham, and the citizens of Atlantis. Aquaman and Mera then share a moment together in the palace where Mera tries to tell him something, when Vulko and Orm interrupt them and tells Aquaman that Ocean-Master and his cult of purists have grown stronger and they still haven't found out his identity. Orm though swears to find him and take him down when suddenly, an army of purists charge into Atlantis and attack all of those they deem "impure". Aquaman, Vulko, Orm, Cal, and the palace guards take them on, but are quickly outnumbered. When some purists start brutally attacking an amphibious teen, 2 Atlantean teen with sorcery abilities saves him.
Aquaman manages to capture a purist and locks him away for interrogation, but not before thanking the teens, who introduce themselves as Garth and Tula, students at the Conservatory of Sorcery. Aquaman thanks them for their help and then heads back to the palace where he and Orm interrogate the purist, but the purist refuses to tell them anything. That night, at his hideout, Ocean-Master meets up with his purists and tells them about his plan to save the captured purist before he gives them away and to get the Trident of Neptune. Later, Ocean-Master uses his royal connections as Prince Orm to sneak the guards in unnoticed. Ocean-Master then heads to the dungeon and frees the purist and then kills him, seeing him as a liability. The purists manage to defeat Vulko and then head to the throne room.
At their room, Aquaman and Mera share a moment as they embrace and Mera once again tries to tell him something, when suddenly, they hear the purists and attack them. Aquaman manages to fight them off, but when a purist manages to capture Mera, he's forced to stand down when Ocean-Master threatens her and then takes the Trident of Neptune. He and his purists then escape with the trident and Mera. Aquaman and Cal then set off after them and while Cal handles the purists, Aquaman corners Ocean-Master and just when he's about to attack him, Ocean-Master casts a spell with the trident, causing Aquaman's evilness to get split into a separate person. The new person names himself Thanatos and quickly defeats Aquaman. Ocean-Master then captures him and has Thanatos go back to Atlantis with Cal and Mera and pretend to be Aquaman.
Back at Atlantis, Vulko and Orm greet "Aquaman", Cal, and Mera and tell them that Ocean-Master somehow managed to trick his way into the palace and has royal connections. "Aquaman" though orders them to call off their search to find Ocean-Master's identity. Meanwhile, Garth meets up with Tula and they introduce themselves and show off their sorcery skills and instantly bond and become friends. Back at the palace, "Aquaman" banishes all "impures" from Atlantis and promotes Orm as his general, despite Vulko and Cal's protests. Later, when Mera tries to tell "Aquaman" the thing she's been trying to tell him, but he blows her off and acts rude to her. Mera, Vulko, and Cal instantly realize that that isn't Aquaman. Later, Garth and Tula find some palace guards brutally torturing an "impure". Garth and Tula stop them, until "Aquaman" orders them to stop and threatens to banish them. Garth and Tula realize that their king isn't the same king they met earlier. Later that night, Garth follows Thanatos to Ocean-Master's lair, where he finds out that Aquaman is locked up and tortured by Ocean-Master and the purists and that Thanatos is an evil clone posing as Aquaman. A purist finds Garth and they attack him, but Garth barely manages to escape by using the "Power of Tempest".
Back at the kingdom, Garth comes back and tells Tula, Vulko, Mera, and Cal about what he found out and they quickly tell Orm about this, but Orm refuses to believe them and leaves. Garth then decides to lead them to Ocean-Master's lair, where they're attacked by purists. They manage to hold them off until Garth frees Aquaman. Mera then unleashes a huge water creation, distracting them long enough for them to escape. They return to Atlantis, where they take refuge in Cal's hut. While unconscious, Aquaman is visited by the ghosts of his parents, Tom Curry and Atlanna, who tell him to find Orm's father, the Atlantean sorcerer, Atlan, who's the only one capable of reversing the spell and destroying Thanatos. When he wakes up, he tells them his plan to find Atlan. Vulko though knows where he is and gives him a map to his hut in the Old Roman's Trench. Garth and Tula volunteer to join him, due to their magical expertise. Cal also volunteers to come, but Vulko and Mera are to stay in Atlantis and keep Thanatos busy while they find Atlan. Before he leaves though, Mera reveals to him that she's pregnant, much to his shock.
Aquaman, Garth, Cal, and Tula then set off for the Old Roman's Trench to find Atlan. Meanwhile, Ocean-Master returns to his lair and his purists tell him that Aquaman escaped. He then uses the trident to kill the guards that were watching him. He then reports back to Thanatos as Orm and orders him to have the entire city be searched for Aquaman. When he has the city searched, he finds a scrap of Aquaman's costume, causing him to believe that Aquaman is dead, so he reveals himself as Thanatos to the citizens of Atlantis and now rules the city like a prison and kills anyone that defies his rule.
Meanwhile, Aquaman, Garth, Tula, and Cal continue their quest and end up being attacked by sharks and squids, but Aquaman uses his telepathy ability to send them away. Aquaman then gets another vision of his parents, who tell him to have Garth and Tula use their magic to help them find Atlan. That night, while Cal falls asleep, Garth reveals to Aquaman and Tula that he comes from a colony and was cast out due to his eye color, where he met Vulko, who took him in and enrolled him in the Conservatory of Sorcery to find his purpose. Tula then reveals to them that she comes from the city-state of Poseidonis and her parents are the king and queen, but never got along well with them, so she left the palace and went to Atlantis, where she enrolled in the Conservatory of Sorcery to become someone other than the heir to the throne of Poseidonis.
Back at his lair, Ocean-Master uses the trident to find Aquaman and realizes they're heading to find Atlan, his father and reports it to Thanatos. He and Thanatos then set off with the purists to stop them. Vulko though realizes where they're going and he and Mera set off to stop them. At the Old Roman's Trench, Garth and Tula use their sorcery and find Atlan's hut, but a rockslide occurs and Aquaman pushes them out of the way, but his hand gets crushed, forcing Cal to slice it off. They then head to Atlan's hut, who uses a spell to make a prosthetic hand out of a fish hook for Aquaman.
They then ask Atlan for help to break the spell and destroy Thanatos, but Atlan is still depressed over losing the love of his life, Atlanna. The spirit of Atlanna though appears and convinces him to help Aquaman. Suddenly, Ocean-Master, Thanatos, and the army of purists arrive and attack them. They take them on, but are outnumbered. Mera and Vulko though arrive and even the odds. Atlan then takes on Ocean-Master, unaware that he's his son, but Ocean-Master doesn't fight back, allowing Atlan to get the trident and he uses it to destroy Thanatos, who is just about to kill Aquaman and Mera. Garth and Tula then use their magic to defeat the purists, but Ocean-Master manages to escape yet again. Aquaman then manages to convince Atlan to return to Atlantis and rejoin society and move on from Atlanna.
Back at Atlantis, Aquaman, Vulko, Mera, Cal, Atlan, Garth, and Tula arrive back. Aquaman offers Garth and Tula to take them on as proteges, but they refuse so they can continue to practice their sorcery. Orm then arrives and lies and says that Thanatos ordered him and his men to the S'atiroman Cave. Aquaman and Mera then share a moment, where Aquaman tells her he's happy to be a father and they kiss. Aquaman then claims his trident and retakes the throne of Atlantis.
In a post-credits scene, in a prison ship, Black Manta is freed and saved by Mercy Graves, who takes him to a private sub, where Lex Luthor steps out of the shadows and offers him the chance to take his revenge on Aquaman, which he agrees. Ocean-Master then steps out of the shadows and Lex offers to help him claim the throne of Atlantis, which he agrees. Lex then welcomes them to the Injustice League and sends Ocean-Master back to Atlantis to retrieve something from the Conservatory of Magic and Science Center in Atlantis as Orm to retrieve 2 "key players" for Lex.