Aquaman learns from an Atlantean doctor that Mera, who is about to deliver his child, will be doomed by a hereditary disease that runs in Aquaman’s family (as will the baby) if she does not receive an antidote made from an anemone root in the Gulf of Terrors, far from Atlantis. The Sea King and Aqualad complete a perilous odyssey to the gulf and get the antidote from an exiled criminal of Atlantis, Sinquo. Mera receives the antidote in time and safely bears their son, Arthur Curry Jr., alias “Aquababy.” However, Aquababy has been given strange powers by the serum, which threaten Atlantis. Aquaman opines that Sinquo added something to the serum that gave his son the out-of-control powers. The Atlanteans demand that Aquababy be taken away from the city, and Aquaman, Mera, Aqualad and Aquababy go into exile. But when the mutant Horrkas attack the family, Aquababy blasts them away, exhausting his powers in the process. Thus, Aquaman and his family are able to return to Atlantis.
While wrangling a rogue giant crab, Aquaman receives word from Atlantis that Mera has fallen ill. In truth, Mera is pregnant. The joyful moment turns tragic, however, when Aquaman's Atlantean advisor, Tumol, explains that, due to a quirk in Aquaman's genetic make-up, Mera and their baby will die upon childbirth. Their only hope is a serum derived from the rainbow anemone, which only grows in the Gulf of Terrors. Immediately, Aquaman and Aqualad set off for the gulf. The journey is long and arduous. En route, each hero reflects on their possible future relationship, with the King's new heir. Aquaman sees his son one day taking over for him, in his role as protector of the sea. Aqualad, more negatively, sees Aquaman's son as a rival who will usurp Aqualad's place as Aquaman's partner. Entering the Gulf of Terrors, Aquaman is beset upon by three sirens, whose song powerfully draws him to them. Aqualad lashes Aquaman to his seahorse mount and leads them both away. As they begin to cross a barren plain, their mounts, Storm and Imp, are suddenly spooked, bucking their riders to the sea floor. Aquaman and Aqualad find themselves sinking into quicksand coral. Despite their great efforts, the heroic pair are unable to pull free and are slowly drawn deeper into the earth.
Aquaman summons a giant squid, commanding it to pull he and Aqualad free of the quicksand coral. Unbeknownst to the two heroes, they have been observed throughout their exploration of the Gulf of Terrors. This sinister witness finally reveals itself. A disembodied voice threatens the two heroes, emanating from a different direction each time it speaks. Suddenly, Aquaman is attacked by a sea snake. As Aquaman grabs the sea snake, it transforms into a sea urchin, and then into a giant poison anemone. Aquaman and Aqualad flee into a coral foxhole. The limited space, however, leaves Aquaman's arm exposed to the anemone. It strikes, depositing all it's poison into his vulnerable limb. The "limb", however, turns out to merely be Aquaman's tunic, stuffed full of broken bits of coral. With it's stingers depleted, Aquaman begins beating the giant anemone with his coral filled glove. The anemone transforms into an old man. He is Sinquo, an exiled Atlantean criminal. For besting him, Sinquo leads Aquaman to the rainbow anemone, providing him with the serum he needs to save Mera, and his unborn child. At great speed, Aquaman and Aqualad set off for Atlantis. En route, the two heroes are caught in an underwater volcanic eruption. Fighting unconsciousness, Aquaman sends out a weak telepathic signal to the surrounding marine life, instructing them to get the serum to Atlantis. From octopus to swordfish, swordfish to eel, eel to whale, an astounding relay of marine creatures transport the serum across the miles. All seems lost though, when an exhausted pilot whale drops the vial of serum into a deep crevasse on the ocean floor.
Mera is near death's door, as time runs out for her and her unborn child. Suddenly, a tiny fish darts into the chamber, carrying the jar of serum. The strain proves to much for the fish, and, seconds later, it dies. Aquaman arrives soon thereafter. In short order, Mera delivers a healthy baby boy. All of Atlantis rejoices at the birth of the King's heir. Waving his tiny hands, the infant conjures a monstrous fish. The creature swims after Aquaman. Using a harpoon, Aquaman locks the creature's jaws wide open, at which point, it fades into nothingness. While touring the construction site of the new royal palace, the child begins waving his hands about again. Beams of destructive force burst forth, destroying the palace, and blasting holes in the dome surrounding Atlantis. Deemed an ongoing danger to the well-being of Atlantis, the Atlanteans demand the child be sent into exile. Aquaman, Aqualad and Mera travel with the child outside the environs of Atlantis. Aquaman sets off in search of food. Mera succumbs to exhaustion, falling fast asleep with the baby. Aqualad watches over them for a time, but he, too, eventually gives in to fatigue. Left unsupervised, the tiny infant is the sole witness to a passing procession of Horrkas, evil mutant enemies of Atlantis. Once more, the destructive beams of force erupt from the child's hands, this time destroying the Horrkas. The power fades away, though, with one Horrka still standing. The Horrka grabs the child, intent on slaying the infant. Aquaman arrives, and after a mighty struggle, puts the final Horrka down. With the child's mysterious powers gone, their exile is lifted, and all return to Atlantis.