Disclaimer: Knowing full well there is a wealth of resources available to fans of the "Justice League" animated series, I have no intention of doing a bunch of dry story synopsis with the occasional new screen grab. I will chronicle, within reason, J'Onn J'Onzz's specific journey over the course of the series, but chiefly I will be reviewing the episodes through my own jaundiced perceptions.
That disclaimer has never before been more true than in this edition. You see, I recall much positive word of mouth from when this Aquaman-related episode first broadcast, and in the years since it seems to have settled into a favorite story of the first season. Too bad it's so awful. The show starts with a 007-style pre-credit sinking of a nuclear sub by Atlantean forces under the command of Namor, the Sub-Mariner. Where in later seasons the JL crew were wonderful about finding the essential appeal of the various heroes they showcased, the first season was all about taking liberties with characters to shoehorn them into a team setting intended for general audiences. I don't understand what demographic they thought hey were appealing to in giving Namor long blond hair, though. The facial hair was also best left to the Jae Lee/90's boondoggle, as well. The pointy ears are present, but in place of winged feet are a couple flippers. I do recognize though that the speedo might not translate well, and his armor does reflect the Kirby stylings of Sub-Mariner's Silver Age appearances, so I guess I can let that slide. He does eventually go shirtless as expected, after all. The earrings are just bad all over.
They introduce lots of political intrigue and backstabbing of the sort you expect in Namor's kingdom, including a scheming sibling. Curiously, they named the usurping kin "Orm," an obvious in-joke for DC fans, as that is the secret identity of Aquaman's villainous half-brother Ocean Master. However, Orm wasn't actually Atlantean, but an air-breather. He practiced sorcery, had black hair instead of brown, facial hair, and a distinct costume. Also, they have Orm trying to kill Namor's son, where with Aquaman, that was exclusively Black Manta's territory. Less amusing was the addition of the aforementioned infant son, plus a red-haired bride. This bride wears a different costume, has no powers, and is mostly a simpering wimp, so no additional confusion with Mera there.
As for Martian Manhunter, he first shows up in silhouette at a satellite viewing deck, listening to Green Lantern and Wonder Woman debate what right Namor had to his attack on the submarine. At Superman's prodding, Namor takes his case to the World Assembly, though with the property damage and arrogant posturing you know has to follow whenever the Sub-Mariner visits New York. The Justice League joins the debate, only to watch as Namor is nearly assassinated by Deadshot. Manhunter looks on as Aquaman is hospitalized, with no sign of their previous friendship from the comics. In fact, I don't recall if J'Onn J'Onzz spoke a word of dialogue until very near the end of the first episode, when he impersonates Aquaman to draw Deadshot out of hiding, "Perfectly." Deadshot looked to have been a proxy for Deathstroke though, as his extensive use of booby traps fells Superman and hinders the rest of the League to a degree Floyd Lawton couldn't have possibly. J'Onn's becoming an immaterial wraith affords him some leeway, but loses him his shot at capturing Deadshot. That victory was ultimately reserved for the recovered Man of Steel. Despite panning to Wonder Woman's hip, when Deadshot refuses to name his client, neither the Lasso of Truth not Martian telepathy come into play. Instead, it's a harsh word from Batman that incredulously makes him crack. Worse, in the meantime, the real Aquaman had recovered and escaped Green Lantern's custody by-- wait for it-- sucker punching him in the mouth. How's that for ingenuity? Namor returned to Atlantis, where he was captured by his own treasonous subject, which is again more of an Aquaman thing.