Summoned to the Pentagon, Aquaman travels to Washington, D.C, aboard a Navy seaplane. There he is shown a video taped television broadcast, of an ultimatum, issued by the Ocean Master. Ocean Master's appearance triggers memories, of Aquaman's first encounter with the famed marauder of the seas. Aquaman and Aqualad had been on patrol when they came across a pod of whales stampeding through a fjord. The pod's terror was so great that they refused to heed Aquaman's telepathic commands to calm down. Diving below the waves, the two heroes spied the root of the pod's fear. An automated whaler had targeted the pod, and was firing a barrage of harpoons into the whales. Aquaman and Aqualad cut the harpoon tow lines, freeing the whales. His whale poaching operation thwarted, Ocean Master recalled the robot whaler to his manta ship. Closing in on Aquaman and Aqualad, Ocean Master began firing on them. Riding Storm and Imp, the two heroes broke for the surface. Ocean Master's manta ship also surfaced, and immediately came under attack by a US Navy destroyer. Ocean Master released fog across the ocean's surface to foil the destroyer's ability to target the manta ship. Covered by the fog bank, the manta ship dove. The Ocean Master had escaped. His reverie comes to a close, as Aquaman returns his attention to the images on the television monitor. In a fantastic demonstration of his power, the Ocean Master, through inexplicable means, strands an ocean liner atop a passing ice berg. Ocean Master threatens to strike and strike again, if the international navies of the world continue to hunt for him.
Journeying to the stranded ocean liner, Aquaman and Aqualad arrive in time to see the ice berg breaking up. Diving below the waves to investigate, the two heroes only turn up a lone sperm whale, following it's migratory path across the oceans. Riding atop a giant manta ray, Aquaman and Aqualad begin searching the surrounding environs in ever widening circles. They re-encounter the same sperm whale. Suddenly, a pillar of salt rises up from the ocean depths, breaks through to the surface, and forms an immense wall, blocking the harbor entrance. Aquaman summons a pod of whales, instructing them to shatter the wall with sound waves, generated by the impact of their tails slapping down against the water. Playing a hunch, Aquaman, instructing Aqualad to follow, dives back down below the waves, in pursuit of the mysterious, lone sperm whale. Alarmed by Aquaman's investigation of the whale, the Ocean Master races to intercept him. As soon as his manta ship is in range, Ocean Master fires a heat seeking torpedo at the two heroes. By swimming past a volcanic vent in the ocean floor, Aquaman is able to divert the torpedo form it's intended targets. A second torpedo is launched, but this one merely circles, around and around, the heroic duo. Suddenly, the torpedo casts a net, ensnaring Aquaman and Aqualad. Brought on board the manta ship, the two captives, at last, come face-to-face with the Ocean Master. Ocean Master explains that he has surgically implanted two devices in the sperm whale. The first device causes random catastrophes via molecular manipulation of the environment, The second device scrambles brain waves, to prevent Aquaman taking telepathic control of the whale. Tied up, Aquaman and Aqualad are placed within Ocean Master's robot whaler. The whaler is then sent to the ocean's surface, where it is immediately targeted, by the US Navy, for destruction.
Aquaman kicks the harpoon release on the whaler, firing a barrage of harpoons into a nearby atoll. As the harpoon lines grow taut, the robot craft is upended, cracking open as it crashes into the coral island. Aquaman and Aqualad use the jagged coral to sever their bonds. Unable to telepathically take command of the sperm whale, Aquaman tames it the old fashioned way. Riding the whale, Aquaman goes after the Ocean Master. As the whale nears Ocean Master's manta ship, the molecular destabilizer implanted in it's body disables the gyroscopic stabilizers on the vessel. Unable to steer his ship, The Ocean Master crashes into the sea floor. Ocean Master exits the wrecked hulk, and prepares to engage Aquaman in combat. Aquaman orders Aqualad to stay out of the fight, insisting on facing Ocean Master alone. Aquaman, however, takes a purely defensive stance in the fight. He dodges and parries every thrust of the Ocean Master's spear, but never once takes any offensive action. Aqualad tries to send in a swordfish to assist in the fight, but Aquaman refuses to accept any aid. Having located the manta ship on sonar, the Navy ships release depth charges on the target. The explosions separate Aquaman and Ocean Master. When the water finally clears, Ocean Master is gone. Returning to the surface, Aquaman gets the Navy to call off the attack, informing them that Ocean Master's ship has been destroyed, and the villain has already fled the scene. He tells the captain that the sperm whale still has to be caught, and to follow a south-southwest heading, along it's migratory route. Aqualad questions Aquaman on his refusal to actually fight the Ocean Master. Aquaman reveals that the Ocean Master is really his half-brother, Orm Curry. Having two human parents, Orm did not possess Aquaman's Atlantean gifts, or powers, and thus, growing up together, bore a deep resentment for Aquaman. His jealousy and hatred for his half -brother would lead Orm down a dark path, as youthful indiscretions led to juvenile delinquency and eventual adult criminal undertakings. Now, to Aquaman's deep regret, Orm had become an arch-criminal, the Ocean Master. The sperm whale is found beached on some rocks. Once Ocean Master's surgical implants have been removed, the sperm whale is returned to the sea. Aquaman is left to ponder what action he will take when next he encounters his evil half-brother.