Quote from Qnjo;1284154:
I don't even know what is season 3 about. Have humans moved to Erinn yet?
Considering that the humans still went to try to finish off the Fomors, probably not. Season 3 revolves around a strange phenomenon, where people are disappearing and no one remembers them just like in the ending of S1/2 (Aodhan, Marrec, and Riordan went to fight Fomors and they just went poof), and Cichol is involved.
I've yet to do Season 3 (as I've yet to finish Season 2), but in the prologue you meet this monster named Muir who seems to know something about the phenomenon, and Brynn's analysis on his body or something leads to a mountain of corrupted elves. (Also plot hole, Brynn leaves his laboratory a couple times, which he's never supposed to do or he'll die.) Cichol appears at one point and says "This is how I'll bring paradise."