The Creatures from Atlantis!
During a morning sea-storm, Aquaman and Aqualad come to the rescue of a cargo ship that's been struck by lightning. When Aquaman finds that the cargo hold broke open and crates carrying a new type of poison are drifting out of the ship, Aquaman and his undersea pals collect all the boxes. Ordering Aqualad to bring all the cargo to shore, Aquaman then returns to his home. There he finds fish with a telepathic message from Atlantis asking for help. Thinking of Atlantis, Aquaman recounts his origins: How his mother was an exile from Atlantis who bore a child with a lighthouse worker. As he remembers how his mother revealed his true nature on his death bed, Aquaman decides to go to Atlantis to find out what he's needed for. Upon his arrival, he is suddenly attacked by two giant humanoid sea-monsters.
Brought into the city, Aquaman sees that the people of Atlantis have been enslaved by this race of amphibious sea-creatures. When trying to demand answers by one of the leaders of these creatures, Aquaman is sentenced to work on the same device the other Atlantians are working on. There he finds out from one of the workers that these creatures came from a "hole" that appeared in the water. Sometime later, Aquaman attempts to start a revolt by summoning an army of sea creatures to come to his rescue, however the creatures have blow guns which they use to turn back the attackers. Later, hiding in a tube close to the creatures, Aquaman learns the truth: They are criminals from another dimension who are building a device that would melt all forms of resistance from the surface world in their bid to conquer the entire planet Earth. Spotted by the creatures, Aquaman is locked up in a cell, but manages to contact his undersea friends, who summon Aqualad with a swordfish to spring Aquaman out of the jail.
Racing to the surface to stop the creatures who are out on a test of their new weapon, Aquaman, Aqualad and an army of sea life attack the monsters. However, they do not stop the creatures from testing their weapons. After a number of attacks, Aquaman orders an army of sea gulls to drop bombs on the creature's vessel rendering it inoperable. The feeling creatures enter an undersea forest, where Aquaman manages to grab hold of their dimensional device and uses it to send them back home. Once the people of Atlantis are free, they reward Aquaman with a Hero of Atlantis medal before Aquaman and Aqualad return to their home in the sea.