A strange submarine is circling Atlantis, and Aquaman goes out to investigate. He catches the ship, only to find himself stuck to its side as Manta-Men pour out of the ship to attack him. He realizes that the ship is a trap to get him out of the city while Manta attacks.
Manta attacks the dome, and Mera and Aqualad realize that Aquaman is in trouble and go out to rescue him.
Manta uses some sort of ray on the waters inside the dome which causes the water to become unstable and boil. Dr Vulko, the leading scientist of Atlantis, orders the dome drained. But because the people in the city can only survive an hour out of water, either Manta must be defeated in that time... or doom for the citizens.
Mera and Aqualad succeed in helping Aquaman, and the trio returns to the city.
They return to a city that has no water. Any attempt to return water to the dome causes a violent reaction. But Aquaman is prepared, and uses Project X, a serum he had Dr Vulko develop that turns all Atlanteans back into air-breathers. Only Aquaman, Aqualad, Mera and Aquababy are spared the shots.
When Black Manta realizes his scheme failed, he leaves the city. Aquaman and Aqualad go on patrol to make sure he is really gone, while Mera and Aquababy hang out with the guards. With Aquaman and Aqualad gone, Black Manta heads back and attacks Mera, knocking her out and stealing Aquababy.
Black Manta gives Aquaman an ultimatum, surrender himself for Aquababy's life. Aquaman agrees and heads toward Manta's ship, unaware that Ocean Master has shown up...
Ocean Master is jealous of Manta's success, so he interferes. He snatches Aquababy, who was supposedly being returned to the city. Manta attacks Ocean Master, who fights back and destroys Manta's ship. Aquaman, trapped inside Manta's retrieval device, frees himself with the help of some whales, only to watch in horror as a last missile from Manta's ship hits Ocean Master's ship.
The Manta-Men attack Ocean Master and Aquababy, and Aquababy uses his hard water powers to defend them. Aquaman attacks Manta, and is shot and at Manta's mercy when Ocean Master attacks Manta. After chasing off Manta, Ocean Master returns Aquababy to Aquaman and leaves in peace.
This issue has the first appearance of Black Manta, though you wouldn't exactly know it as Aquaman recognizes him and the Manta-Men. It is possible that this issue came out after the first Manta episode of the Aquaman TV show, though I doubt it as the first episode was aired September 9, 1967, and this issue was cover dated Sep-Oct 1967. Since comic books generally come out before the cover date, this issue should have been on the stands when the show debuted.
Mera makes good use of her powers in this issue, including a hand that opens the gate for her and Aqualad, and a hammer that frees Aquaman from the trap.
This also features the first appearance of Vulko, who is referred to as "Dr Vulco" on page 5, then as "Dr Vulko" on page 7 and thereafter.
It's important to note that the citizen of Atlantis become air-breathers in this issue. They don't go back to being water-breathers for several issues. In issue #40, Vulko comes up with a way to get rid of Manta's chemical in the dome that reacts with water. In issue #41, Vulko perfects an antidote to Project X. In issue #43, the antidote is finally administered, and things in the city get back to normal.
Ocean Master's memory seems clearer in this issue, although he doesn't remember that Aquaman is his half-brother, he does spare him when he could've killed him and Aquababy.
The letter column was mostly about Aquagirl, and issue #33. Most of the comments they printed were positive.
Shorts and notable ads in this issue: a half-page Cap's Hobby Hints cartoon, a two-page cartoon ad for Mattel's Major Matt Mason toys, and a one-page Direct Currents (with ads for Wonder Woman #172, Jimmy Olsen #105, and Green Lantern #55, among others).
This story is reprinted in DC Super Stars #7 (Sep 1976).
First appearance of two of the best supporting cast members, and lots of other fun thrown in.