Located in the eastern Atlantic not far off the west coast of Africa, Poseidonis is a large underwater city-state.[1] Both the Conservatory of Sorcery and the Science Center are located here, and it is the seat of power of the High King of Atlantis. The main city is divided into five sectors, though the Royal Palace does not belong to any of them.[2] As well as being the Atlantean capital, it is also the wealthiest city-state, a cause of resentment among other Atlantean states.[1]
At a time when Orin was absent, Black Manta attacked the capital. It caused severe structural damage, but the main objective, securing the echinoderm in the Science Center, was only partially achieved.[2]
While talking with his old friends Garth and Tula, Aqualad learned about the purist uprisings. They had to break up a row between conservatory students about that very subject.[3]
Miss Martian traveled to Atlantis's capital to meet up with Lagoon Boy, who had been living in the city to recuperate from wounds sustained three weeks earlier. They left in the Bio-Ship together.[5]
Aquaman brought a water-breathing meta-teen through the Zeta-Tube to start her new life in Atlantis. He cast a translation spell to allow her to communicate. He later introduced her to King Orin before taking her to meet his parents in Shayeris, where she would be staying.[6]
The Conference of Delegates resumed, with Bishop Beluga representing Xebel. After some discussion, the Conference, and the whole city, came under attack from Ocean-Master, who could only be driven off by a mysterious stranger, who disappeared as quickly as he arrived. Poseidonis was heavily damaged in the attack.[1]
Kaldur'ahm and La'gaan reported to King Orin in the ruined conference chamber about their lack of success finding Ocean-Master, and the growing unrest in other city-states. May saw wealthy Poseidonis being unfairly favored, though the cost of repairs following Ocean-Master's attack was being met by the city's own General Fund, not the Atlantean Treasury.
At Kaldur'ahm and Wyynde's house, Kaldur called his parents, but was interrupted by the commotion caused by the creation of a pillar of fire in the ocean just outside the city.[7]
Mera responded to Child's pillar of fire as Doctor Fate, Zatanna and her students teleported nearby, then left once they saw Child was gone.[8] Mera was joined by Kaldur'ahm and Orin. Later, Ocean-Master appeared to help quell the pillar, but only when the stranger arrived and all three worked together was the pillar extinguished. Ocean-Master attempted to kill Kaldur and Mera but was defeated and taken into custody. The stranger reluctantly revealed himself to be Arion, former Lord of Atlantis. The events caused the people of Poseidonis to begin talking about the prophecy.[7]
At the Science Center, Arion was tested to confirm his identity, with inconclusive results.
Later, crowds had gathered outside Arion's residence, representative of growing support for him to become High King.
Elsewhere, Orin ordered Kaldur to take a squad on a covert mission to the Undersea, a pocket ocean beneath Xebel that the Watchtower had detected. Orin hoped he would find Arion's crown, allowing them to settle both the prophecy and "Arion"'s identity.[9]
At their respective homes, Kaldur and La'gaan prepared to leave for the mission, though their significant others were unhappy with their decisions to go.
Orin visisted Ocean-Master in his prison cell. Orm's responses made Orin dubious that he really was Orm. Orin later assigned Blubber to test Ocean-Master's mask for DNA to confirm his identity, then left to conduct his own investigation.[9]
Poseidonis June 02, post-15:07UTC-2
Chian informed Arion of the chaos in Xebel, and urged him to take action, offering to sneak him out.
Orin visited a seedy bar in Ninth Tride to speak to Ocean-Master's former lieutenant, Danuuth. Orin then returned to the palace and explained his doubts about Orm, which were fully confirmed when Blubber arrived and told them he had found Orm was a clone. Mera told Orin that Arion had disappeared.[9]
Orm called for Miss Martian to help him find the truth. She recovered his first true memories, confirming that not only was Orm a clone created by the Light, so was Arion. Arion also had Orm's memories and was to be his true successor, with the clone Orm as an expendable patsy. By the time Miss Martian was able to inform Orin, the Conference of Delegates had already elected Arion as High King, and Orin did not think anyone would believe the truth.[10]
Poseidonis July 3, 19:36UTC-2
"Arion"'s first speech as High King was broadcast throughout Atlantis, including in Posedionis. After "Arion" was killed for donning Arion's crown, Mera was made High King. She then broadcast her own speech, which was cheered by the people of Poseidonis.[10]
Kaldur greeted Rocket and Nightwing at the Zeta-Tube. He had finished his leave to deal with Conner's death, but his friends told him they had reason to believe he was still alive, and recruited him for their investigation.[11]