In pursuit of the octopus that kidnapped his son, Aquaman is ambushed outside the city of the Idylists. Aquaman's Idylist escorts refuse to aid him in the combat, as they are pacifists. Aquaman's trio of attackers are on the verge of besting him when the Sea King summons aquatic aid to turn the tide. The villains are identified as being loyal to the usurper who has taken control of the Idylist's city. Upon entering said city, Aquaman feels a strange sensation, but has no time to dwell on it, as he is spotted by more of the usurper's minions. Eschewing a long, protracted battle, Aquaman immediately summons a passing hammerhead shark for assistance. To his astonishment, the shark disregards Aquaman's telepathic commands, instead battering the Sea King into unconsciousness. Meanwhile, NATO commander, General Horgan, engaged in conversation with Ambassador Diaz, regarding the disappearance of four prominent diplomats, is kidnapped by the Fisherman. Aquaman awakens to find himself chained to a wall, along with Aqualad and an Atlantean, McAan. Years earlier, McAan's son had run away, following a band of Idylist cultists back to their city. Mistaking Aqualad for an Idylist, on account of his purple eyes, McAan attacked Aqualad, demanding the teen hero take McAan to the Idylist city, and his son. Aqualad aided McAan in locating the Idylist colony's fabled "City of the Lost Tribes", only to find it under the control of the Black Manta. Aquaman's old enemy has chosen the Idylist's colony as the foundation stone for his new empire.
The Black Manta unhooks Aquaman from the wall, to beat the Sea KIng, while explaining his intentions between blows. Feigning great injury, Aquaman is able to momentarily gain the advantage, and opts to escape. Exiting the makeshift prison room, Aquaman is beset by angler fish, that grapple him long enough for a school of needle fish to try to spear him. Aquaman narrowly avoids the needle fish barrage, and ducks into a nearby building, with the Black Manta and his minions in hot pursuit. Aquaman finds himself in an operating bay, where Idylists are surgically grafting gills onto the Black Manta's air-breathing minions. Aquaman rushes to turn one of the medical lasers against the Black Manta, only to be stopped short by the Black Manta's revelation that Aquaman's infant son is his prisoner. Aquaman surrenders. In short order, Aquaman and Aqualad are brought into an arena. The Black Manta has Aquaman's son placed in a glass sphere, one that is slowly having the water drained out of it. When either Aquaman or Aqualad has been killed, the Black Manta will replenish the water in the sphere, keeping the child from suffocating to death. Aqualad leaps to attack the Black Manta, only to be repelled by a force shield surrounding the arena. With his son's life at stake, Aquaman viciously attacks his sidekick, quickly drawing blood. A brutal battle ensues between the two partners, with no quarter asked or given.
When Aqualad slams Aquaman back against the force shield, a hapless grouper is caughtt between Aquaman and the shield. The grouper begins acting erratically, leading Aquaman to the realization that the reason the fish have been obeying the Black Manta is because they're all robots. The strange sensation Aquaman experienced, entering the Idylist's colony, was a sonic barrier the Black Manta erected to keep out the real fish. The only real fish is Topo, the octopus that brought Aquaman's son to the colony. Aquaman telepathically commands Topo to grab and destroy the Black Manta's control device. As the force shield goes down, Aquaman hurls his trident at the glass sphere imprisoning his son, to let in the life giving waters. The Black Manta imperils the Idylists, to buy himself time to escape. After Aquaman has saved the Idylists, he is approached by a woman carrying his son. Aquaman's rescue came too late for little Arthur, Jr. The infant suffocated in the air filled sphere. Aquaman is filled with anguish and rage at the murder of his son. Aquaman instructs Topo to take the body back to Atlantis, then gestures for Aqualad to join him in the hunt for the Black Manta. Aqualad, however, refuses. His mentor had just tried to kill him, and Aqualad decides that, however justified those actions were, it would be best if they parted company for a time. Aqualad resumes the search for McAan's missing son, while Aquaman heads off in pursuit of the Black Manta.