A fisherman reels in Lori Lemaris. His dreams of exploiting her are shattered when she moans Superman's name. Hours later, Superman flies to the Metropolis location of S.T.A.R. Labs, where Doctor Klyburn leads him to Lemaris. Superman's former flame reveals that her city, Tritonis, was viciously attacked by it's sister city, Poseidonis. Even more shocking, Aquaman was leading Poseidonis' charge against Tritonis. Superman accompanies Lemaris to Tritonis, to get some answers. Mistaking the pair for scouts from Poseidonis, Tritonis' city guard fires on them. Superman blocks the shell, then swaddles Lemaris in his indestructible cape, to protect her from shrapnel. Superman thrusts his arm down the cannon's maw, causing it to backfire, thus destroying it. The attack is called off once the city guard recognizes Lemaris. Superman finds the city of Tritonis fortified against further attacks. The populace is clearly preparing a retaliatory strike. Before it can happen, Superman journeys to Poseidonis to determine why, exactly, these two formerly peaceful cities are gearing up for war. En route to Poseidonis, Superman is attacked by a giant squid. Then a school of eels. Then seemingly every fish in the ocean surrounds the Man of Steel.
Superman swims at super speed, in a tight circle, generating a whirlpool that sweeps the fish away. Coming to a stop, Superman finds himself face-to-face with Aquaman. The Sea King's tale differs from Lemaris'. Aquaman and Mera were relaxing in the Aquacave, when what they believed to be a seaquake occurred. Investigating the matter further, Aquaman discovered that Posiedonis had come under attack. King Vulko could not identify the invading armies. Aquaman took a patrol to Tritonis to see if it, too, had come under attack. Upon arrival, Aquaman found his forces being fired upon by the Tritonis city guard. Aquaman's story completely contradicts the one told by Lemaris, leading Superman to believe that an outside party is manipulating them all. Superman and Aquaman return to Tritonis, but are refused entry at the gate. Superman forces his way inside. Superman and Aquaman are immediately set upon by the city guard. At first, the two heroes put up a fight, but then decide to surrender. They are brought before the new ruler of Tritonis, Aquaman's half-brother, the Ocean Master. The pacifistic populace of Tritonis were ill-prepared to wage war with Poseidonis, and thus made Ocean Master their king, believing he could protect them.
Ocean Master sentences Aquaman to death, but defers carrying out the sentence in Superman's presence. The two heroes depart Tritonis. Outside the city, Aquaman reveals that something in Ocean Master's throne room was dominating the wills of Tritonis' citizens. Superman digs a tunnel,down into the sea bed, coming back up in the throne room. Ocean Master, however, is waiting for them. Aquaman turns to attack his half-brother, but suddenly collapses in agony. Ocean Master shatters the globe in the center of the room, releasing an enormous jellyfish, which immediately attacks Superman. Despite his best efforts, Superman cannot escape the creature's tendrils. In fact, the harder he struggles the stronger the monster seems to become. With the creature focused on Superman, Aquaman is able to recover. He begins pummeling his half-brother with a rain of haymaker blows. Realizing the creature feeds on aggression, Superman ceases struggling. The creature continues to maul the Man of Steel, until it's reserves of strength evaporate, at which point, it collapses. Aquaman finishes beating Ocean Master into unconsciousness. On Aquaman's recommendation, Superman carries the creature out to the depths of the Marinas Trench. Ocean Master is taken to Poseidonis for incarceration. With it's people liberated form Ocean Master's subjugation, Superman and Aquaman bid their farewells to Tritonis.