Aquaman and Aqualad visit Ocean Colony Alpha, the first attempt by air-breathers to colonize the ocean. This colony is growing with the help and support of the Atlanteans.
Off in space, meanwhile, a strange device approaches earth. Launched from a dying planet many years ago, it now plants a city on the ocean floor near Alpha Colony. The city of Necrus recognizes the threat the colony constitutes, and orders go out to destroy it. The colony is destroyed, witnessed by one Atlantean survivor, who reports the return of the black city to Aquaman.
Aquaman explains to Aqualad that Necrus is a city of evil beings that occassionally appears on the ocean floor. It is ruled by the evil Mongo, and Aquaman has battled them repeatedly in the past. Aquaman doesn't know that Necrus' appearing and disappearing act is caused by the orbiting device whenever it comes back into range of Earth.
Aquaman uses his spy network of fish to find the black city, and swears revenge on it for the destruction of the colony.
Mongo sends out a giant android to battle Aquaman, who retreats until he can figure out how the android works. But a shark sees Aquaman in danger and attacks the android. Aquaman and Aqualad go to its rescue, and Aquaman is captured.
Brought before Mongo, Aquaman tells the leader that he has sworn revenge for the destruction of the colony. Mongo asks Aquaman why he allowed air-breathers to invade the oceans. Aquaman says there is plenty of room, and refuses to ally himself with Mongo.
Aquaman is put in a crystal sphere prison. He goes along the ocean floor, knowing that Mongo will soon attack Atlantis, until he spots a strange beam that is changing coral. He moves the sphere into it, hoping it will break him out...
Back in Atlantis, the hosts of Necrus are attacking and Aquaman isn't around to lead the city's defense. Aqualad takes command, but is interrupted by... Aquaman! Mongo is surprised to see Aquaman leading the Atlantean defense. Aquaman seems to be leading the Atlanteans into disaster though, as Mongo attacks...
Aquaman's finy friends raise a net of sea grass that traps Mongo's troops, and allows the Atlanteans to battle them easily. Mongo leads a commando troop into Atlantis and grabs Mera, who can't use her powers with her arms full of Aquababy. When Aquaman arrives, she launches Aquababy at him, then uses her powers to conquer Mongo's troops.
Mongo flees, with Aquaman chasing him, and Mongo pushes Aquaman's head into a wall, knocking him out. Not just out... dead. Although Mongo's troops are defeated, Aquaman is dead. Mera announces the sad news to the people, and many heroes from the upper world arrive for the funeral.
Mongo, a fugitive wandering the ocean floor, spots Aquaman, very much alive, still in his crystal cage. Mongo frees him, and demands to know how Aquaman was in two places at once. But as he threatens Aquaman, a hard-water hand comes out and destroys his weapon. It's Mera, who knew that the second Aquaman wasn't real because his kiss didn't feel right.
Aquaman explains that the duplicate split off when he went into the strange beam, and he was able to control the duplicate and lead the defense of Atlantis, even though he was always inside the sphere.
While they talk, Mongo flees back to Necrus, and the city vanishes again.
The "Q" in Aquaman is a wreath on the cover, and the whole title is draped in a black cloth. Aquaman's pall-bearers are Batman, Metamorpho, Superman, and Hawkman. Wonder Woman is in the background comforting Mera.
The mystery of Necrus isn't solved by Aquaman in this issue. I want to know if Necrus and Mongo have appeared before, and where.
Aqualad was taking charge, willing to try to fill Aquaman's shoes, and was doing a darn good job at it, too, when Aquaman re-appeared. I was almost disappointed that Aqualad didn't get to lead the city's defense.
The one panel funeral scene has Superman, Batman, The Flash, and Hawkman as Aquaman's pall-bearers.
The letter page title this issue is "It's a Deluge!". There were eight letters, and if there was a hot topic, it was the subject of Aqualad getting a girlfriend.
Shorts and notable ads in this issue: a half-page "Cap's Hobby Hints" cartoon, and a one-page public service cartoon on staying in school.
A surprisingly good story, with a villain for the ages and neat little cameos.