Each book tells one Warrior's story as he fights the evil vamps or fae or werewolves, and meets up with his twenty-first century soul mate along the way—frequently (but not always) a human. The story arc for the series features the warriors' search for the gems from Poseidon's trident, which were scattered over the world when Atlantis sank. When all of the stones are retrieved, Atlantis can rise again (but not before all of the Warriors meet their soul mates and achieve their HEAs).
According to a page on the author's web site, "Heart of Atlantis will be the final book in the first arc of the WARRIORS OF POSEIDON series. But don't worry! I promise to write Denal's book and Jack's book!" On another web page, Day promises that there will be more Atlantis-world novellas and that Jack will be getting his own series, with news of that coming later in the year.