Doctor Cyrus Beard invents a device that evolves animals into water-breathers. The test animals, however, become savage after undergoing the treatment. Beard reverses the effects, and returns to his research. Weeks later, a stunning migration of land animals is spotted entering the sea, from every coastline. The savage beasts attack a cargo ship, sinking it. In response to the ship's distress call, Aquaman and Aqualad arrive. Aquaman quickly discovers that the animals, despite their aquatic characteristics, are unresponsive to his telepathic control of marine life. Aquaman summons a school of sharks to ward the animals off. Using their tusks and trunks, the elephants hurl the sharks away. With the freighter crew safe, and the animals moving out to sea, the Aquatic Aces attempt to recover the ship's cargo, only to find the holds empty. Beard summons Aquaman, revealing that he is the cause of the animal attacks on the shipping lanes.
Somehow, his mutagenic compound has contaminated the water supply, along every coast on Earth. Beard provides Aquaman with a weapon to reverse the evolutionary effects on the animals. Aquaman catches up with the hordes of animals, as they lay waste to another cargo ship. Aquaman pulls the trigger on Beard's weapon, but nothing happens. Aquaman and Aqualad do their best to distract the animals, while the ship's crew flee to safety. Attempting to salvage that ship's cargo, Aquaman, once again, finds the holds empty. Aquaman notices a clump of seaweed that was also at the scene of the previous ship's sinking. Investigating, Aquaman discovers that the seaweed is concealing a diving bell, piloted by Beard's assistant, Kirk. It was Kirk who used Beard's device to mutate the hordes of animals into a savage herd, then steered them towards cargo ships.
Kirk followed behind the horde, looting the sunken freighters of their valuable cargo. Kirk lashes out at Aquaman, with the diving bell's claw. Chasing Aquaman and Aqualad to the surface, Kirk herds them towards a horde of savage Hippopatamuses. Aquaman and Aqualad elude the beasts, and Kirk, by swimming into a narrow crevasse. Unfortunately, the crevasse is filled with smaller, but no less savage, animals. Aquaman hurls a rock at the diving bell. The Hippopatamuses pursue the rock, inadvertently destroying the diving bell. Aquaman carries Kirk to the surface, with the animals right on his heels. Aquaman lures the savage hordes to the coastline. With the mutagenic element recovered from Kirk, Aquaman reverses the power on Beard's device, restoring the animals to normal. Returning the device to Beard, Aquaman gets the inventor to promise not to experiment on anything bigger than laboratory mice in the future.
The image of a ship in distress leads Aquaman and Aqualad into a trap. As the illusion of the ship fades, the Aquatic Aces are drawn from the sea by a tractor beam. The two heroes are deposited into an enormous tank, filled with the aquatic denizens of dozens of other worlds. The tank is towed to an alien world. There, Aquaman, and the other captives, bear witness to a host of gladiatorial games. After their tank is brought into an enormous underground complex, Aquaman, Aqualad, and the other captives are given energy lances, and instructed to train for the games. While sparring, Aquaman observes the fantastic abilities of his fellow captives, as they try to kill one another. Aquaman convinces them that, by working together, they can all win the chance to return to their respective worlds. The tank is wheeled into an arena, and the order is given for the aquatic men to fight.
For long moments, Aquaman, and the others, play at combat. Then, as one, they turn their "steeds" to the tank's wall, and shatter it, with concentrated fire from their lances. Aquaman orders the alien, called "Styz", to increase his body temperature. The water from the tank boils into steam, providing the escapees cover in which to flee. Aquaman orders the alien, called "Myrot", to use his ability to manipulate and control water, to form a column next to a tall buliding. Aquaman swims up the column, to reach the rooftop. From there, Aquaman is able to ascertain the location of the space port. Aquaman swims back down to the street, only to find his companions, including Aqualad, have vanished. Suddenly, Aquaman is drawn inside a truck. There, Aquaman finds his missing companions. Aquaman meets Starra, the leader of an opposition movement to the alien world's dictator, Tiros.
Aquaman offers to kick off the revolution, if Starra will finish it. Aquaman orders the alien, called "Xuvia", to serve as Starra's bodyguard, as Xuvia is covered in protective scales. Drawing from several lakes, Myrot propels Aquaman's team through the streets, within columns of water. Using the weapons provided by Starra, Aquaman, and his associates, lay siege to the city. Aquaman spies Xuvia racing towards the tyrant's arena. Aquaman confronts Xuvia. The treacherous alien intends to inform Tyros on where he can find Starra's opposition forces. Aquaman fights a defensive battle against Xuvia, eventually tricking him into falling into a deep pit. The weight of Xuvia's scales will not allow him to climb the pit's walls. Should Xuvia retract his scales, however, he will be no match for Aquaman. Once Starra's opposition forces have overthrown Tiros, Aquaman, and his companions, are returned to their respective worlds.