Part 1: The Battle of the Rival Aquamen
Aqualad is waiting for Aquaman and Mera near a lighthouse, when a wave comes and lifts the lighthouse out to sea. Aqualad has Topo rescue the lighthouse keeper, then confronts the culprits: Aquaman and Mera.
The pair attack Aqualad, who retreats hastily, but is about to get captured by Mera... when Mera saves him, and Aquaman drags him down into the depths. Apparently there are two Aquamen, and two Meras. Aquaman thinks the dopplegangers are fantastic robots, and has a plan.
While Aqualad distracts the doubles, Aquaman and Mera sneak up behind them and attack. But the doubles vanish as they are held, and Aquaman suspects they aren't robots after all. As they wonder, a stranger with a gun approaches them...
Part 2: The Aquarium of Space
The stranger is an alien, Xen, from another solar system who is collecting species for his intergalactic aquarium. Usually the duplicates are able to capture his specimens, but this time stronger measures are called for. Xen creates giant duplicates that go after the trio.
Aquaman and Mera easily defeat their own duplicates, but forget there is a giant Aqualad too. The giant Aqualad captures the three and takes them to the alien spaceship, where water-beings from Jupiter, Saturn, Pluto, and Mercury are held.
As they take off, Aquaman asks the other if they've tried to escape. They say they've tried many times, and never succeeded. The ship launches...
Part 3: The Underwater Round-Up
Aquaman calls sea eagles to bring squids to the ship, and spray black ink over the view shield. Underneath the ship, more fish build a hasty set of sharp coral spikes to break through the holding tank, freeing the captives. They escape the stun guns under the cover the the shell of the Saturn alien, and disappear into earth's oceans to regroup and plan.
Xen duplicates himself many times and sends his own duplicates to capture the group. They battle the duplicates and let Mera and Aquaman sneak off to capture the duplicating gun, make a giant Xen under their own control, and save the day. The "local" aliens make obedient Xens to fly the ship back to their home worlds, and Mera gives Aquaman a kiss.
Another striking cover, with Aqualad, Aquaman and Mera being menaced by giant versions of themselves.
The "local" aliens are: The Blubber Man from the waters of Jupiter, the Shell-Back Man from the Lakes of Saturn, The Eel Man from the Plutonian Oceans, and the Fluorescent Water Man from Mercury.
This story was almost certainly written and pencilled before the wedding of Aquaman and Mera. There is no mention of them being wedded, except for a "honey" from Aquaman to Mera. Aquababy is nowhere to be seen. Aquaman reacts with shock at Mera's kiss, and the three parts have individual titles, which hasn't happened since the wedding issue.
The second ever Aquaman letter column, titled "More About Your Letters" and featuring the tag line "We Must Be Doing Something -- Write!". The first letter is about the growing Aquaman family, and Aqualad's role in it. The second asks who the creative team is. The next three letters are about specific issues, and the last letter, left unsigned, is a call for a title for the Aquaman letter column.
Shorts and notable ads in this issue: an ad for the Superman cartoon on TV caught my eye (I looked for my local station), there is a half-page "Cap's Hobby Center" cartoon, a half-page Direct Currents column, another Cheerios ad (full-page) featuring Rocky and Bullwinkle, and a one-page public service cartoon on health myths.
A very Silver Age story, with typical silly aliens.