The Atlantikoinonia is a secret society founded by Artemis. Its mission is to eradicate all evidence that Atlantis and Apollymi ever existed. Artemis claims that this is to protect Acheron Parthenopaeus, but he believes she just doesn't want anyone to know about her association with him.
In Acheron, they attacked Nikolas, a member of Tory Kafieri's excavation team, in Greece and stole artifacts from him. They tortured and killed Dimitri, another man on the team, for the location of one of Ryssa's journals. They also gave orders to kill Tory on sight. Several men shot at Tory and Acheron while they were riding his motorcycle, then ran over him. At the end of the book, Artemis called off the Atlantikoinonia and Tory agreed to stop searching for Atlantis.