Topo desperately tries to flee from hooded pursuers. He unleashes a dose of ink to cover his escape to a nearby cave, but before he can even catch his breath, he realizes his enemies have already cut him off.
The Team returns to the Cave after a mission. Artemis, Robin and Kid Flash prepare to head home in the Zeta-Tube. Before activating, Artemis asks Aqualad if he needs any help, but he answers that it's not necessary, and that he'll head home himself.
As soon as his friends have left, Aqualad turns to Miss Martian and Superboy, and asks them if they would like to join him on his trip to Atlantis. He had waited with the question until the others had left because their bodies could not withstand the pressure of the ocean.
Before showing his teammates Poseidonis, Aqualad stops by his home in the city-state Shayeris. Superboy notices Miss Martian is shorter than usual; it's the water pressure. Even the Bio-Ship is smaller. Aqualad offers them swimwear and rebreathers, but only Superboy takes them; Miss Martian shape-shifts gills like Aqualad's to allow breathing.
Aqualad introduces his parents, Sha'lain'a and Calvin Durham, who are pleased to meet their son's friends, but are surprised they both speak Atlantean. Miss Martian explains she can psychically translate languages, while Superboy mentions his education by G-Gnomes. Calvin takes his son aside, and warns him about trouble in the capital.
Queen Mera greets the Team in the throne room. Once they have all exchanged their gratitude, Prince Orm arrives. He is still protective of his sister-in-law, especially now that she carries the heir to the throne in her womb and with Orin is away, "playing Aquaman". Orm tells Kaldur there is unrest, especially at the Conservatory of Sorcery.
At the Conservatory, Aqualad greets some of his old classmates: Blubber, La'gaan, Nanaue Sha'ark, Ronal and Lori Lemaris. Miss Martian remarks the diversity of the group. Aqualad explains the origin of the nation: a millennia ago, Atlantis sank, and the Atlanteans used sorcery and science to adapt to their new surroundings. Over the years, inhabitants of each of Atlantis's city-states evolved. It is a nation of diversity, and Poseidonis is the most diverse. La'gaan wants to know about the surface life, but gets little answers. Miss Martian notices the mermaid Lori, and changes her legs into a tail. Lori claims she's flattered, but her look suggests otherwise. Ronal leaves, which leads to mockery from Nanaue because Ronal would feel "outnumbered". Garth and Tula arrive, and Miss Martian realizes why Aqualad wanted them with him: he's still in love with Tula and doesn't want to face her and Garth alone. Kaldur seeks out one last old friend to meet—Topo. However, Topo doesn't want any contact. Aqualad quickly learns why: the word "MIΓAΣ", "impure", is etched in his chest.
Aqualad inquires with Garth and Tula about Topo and his injuries. They explain to him that he was a victim of the purists, a group of activists who wish to cleanse Atlantis of its "impurity"—those with visible aquatic features. Aqualad wants to know more, but they overhear an argument between King Sha'ark and Ronal, and investigate. La'gaan and Lori accuse Ronal and his friends of being purists. Aqualad and his friends intervene, but both sides accuse each other of starting the fight. Lori accuses Ronal and his friends of being responsible for Topo's scars, though the victim wishes to be left out of the conflict. Both parties eventually split up after Kaldur, Tula, and Garth threaten to use magic.
Atlantic Ocean September 6, 20:09UTC-2
Ronal and his friends report back to Ocean-Master. They're disappointed Aqualad intervened, as the students would have been marked if he hadn't. But Ocean-Master insists on secrecy; it is their greatest weapon. Their master plan is moments away from succeeding. Now that Orin is away, they can cleanse Poseidonis of impurity. When the king, himself pure, returns, he would surely accept the necessity of the actions.
Lockhart and Morrow are at the Queen Memorial Cemetery digging up a coffin. Lockhart complains because he has to do all the work, but Morrow ignores it. They exhume Danette Reilly, the former heroine Firebrand, who was killed more than sixty years ago.
Poseidonis September 6, 23:45EDT
As Queen Mera sleeps, purists make their way towards the palace. They take out one guard; another betrays his post and joins his purists friends. Mera wakes to the noise, only to find Ocean-Master in her bedroom, his trident aimed at her head.
To Be Continued
The title has several interpretations, both literal and figurative meanings. The plot takes place in Atlantis, which is underwater—literally under the surface. T.O. Morrow and Jim Lockhart exhume the body of Danette Reilly, which is buried under the ground. Also, the Atlantean purists are discriminating against and targeting "impure" Atlanteans for their inhuman attributes. So, figuratively speaking, they judge others by their "surface" and not by what's underneath. Finally, the identity of the man underneath the costume of Ocean-Master is revealed to the reader.