Aqualad, Superboy and Miss Martian prepare for the night in Atlantean sleeping pods. Both guests are comfortable with the local custom, though Superboy does not like them being called "pods". As the lids close, Queen Mera magically reaches out to Aqualad, telling him she's in danger.
They rush to the throne room, where they intercept Ocean-Master and his purists. A few are taken out, but they make it outside. With the spells of the palace no longer barring his use of magic, Ocean-Master orders his henchmen to take the queen away, and takes out his pursuers with his trident.
Prince Orm wakes the young heroes, and briefs them on the situation. His sources have pointed at two locations for possible purist strongholds. He will investigate one himself, with some loyal palace guards, while Aqualad and his friends can go after the other location.
Chained to a table, Mera questions Ocean-Master's motives. He is honest with her: he wants what he believes is his, and Mera's power too.
At the Old Roman's Trench, Aqualad, Miss Martian and Superboy are pinned down against the mountainside by purist magic. However, Aqualad had thought of providing back-up: his old friends from the Conservatory of Sorcery attack from behind, and engage the purists. Lori Lemaris has her hands full restraining King Sha'ark, who is eager to eat his opponents.
Ocean-Master continues to drain the life force from the queen, and charges his trident with a chant.
The purists are mostly defeated, but as Garth claims victory, a mysterious substance in the water weakens the students. King Sha'ark lies motionless, but as a purists wants to kill him, they both are surrounded by a black fog. Topo swoops in and carries Sha'ark to safety. Superboy is the only one who can still see, using his infrared vision to single out the combatants. But they're too weak to fight them, and the purists escape. Miss Martian tracks some, and finds them at the S'atiroman Cave. Tula wants her and Garth, the only ones unaffected by Ocean-Master, to lead the fight, but Lori strongly disagrees. If two "pure" Atlanteans were to do the fighting for the "impures", it would only fuel the purists' misconceptions.
Ocean-Master reveals his intention to Mera: he does not simply want to purge Poseidonis of the impure to rule, he wants to cause civil unrest in the other impure city-states that can lead to a civil war. Ronal overhears this, and sheds his cape to abandon the purists. He may have been prejudiced, but he will not betray king and country. Ronal tries to attack the villain, but with the powered trident, Ocean-Master deflects the hard water attack and sends it back at Ronal. Miss Martian, who had been hiding, tries to telekinetically remove the trident from Ocean-Master's hand, but is found out. He boils the sea around her. Aqualad and the others arrive, but Superboy is almost immediately taken out of the fight when Ocean-Master destroys his rebreather. The rest are pinned down by another hard water creation, a giant octopus. Garth summons the power of the tempest, which knocks back Ocean-Master and causes him to temporarily lose hold of the trident. With his main power gone, he is forced to retreat.
Poseidonis September 7, 07:01UTC-2
At the Conservatory of Sorcery, King Sha'ark has to be held back when Ronal returns. He cannot believe King Orin has granted the erstwhile purist a full pardon, but Topo forces him to stand down.
King Orin, just back from his mission with the Justice League, thanks Aqualad, and Orm vows to find out who gave the false tip that lead to the ambush. Aqualad wishes to return to the surface world, because Miss Martian and Superboy will start school later in the day.
The title of this issue serves as a conclusion of last issue's title. Before all the globe had been explored, cartographers would write "here be monsters" (or variations thereof) on unexplored parts of the map. The monsters in this issue could be, depending on the point of view, either the Atlantean purists or the "fish-heads".
When Miss Martian tries to take Ocean-Master's trident with telekinesis, he asks "What sorcery is this?". Goliath said the same thing when he saw his clan in stone sleep during the day, in the episode "Awakening" Part Two of Gargoyles, another show produced by Greg Weisman, who also wrote this issue. This line was uttered three more times on that series.
A few pages before, one hooded purist paraphrases the line, saying "What new sorcery is this?" when Topo spouts his cephalopod ink to confound the engaging purists.