FM-DrowJournal

Reading through the book you retrieved from the drow woman, it appears her name was Shalana.  The book reads more like a spy's notebook about her rivals.  While most of the details about her previous activities are no longer useful since you've thwarted all her plans, her notes about her rivals on this island are much more useful.  They all seem to be trying to curry the favor of a Great Evil One who is trapped on this island and will give power to whoever can free him.  Obviously, they're all looking to betray him, of course.
The Great Evil One lives in the Shining Palace in the center of the island.  He is very inhospitable; doesn't like guests, especially if they are uninvited; and has control over the Arcane Gates for the island.  He has given the potential heirs for his power the holy weapons that are to be used to corrupt the holy sites via a magical ritual.
Shalana worked for a woman that lived in the Magma Swamp, a very inhospitable place that didn't like to let people in or out.  The woman's skill with magic and charm was unparalleled, and a surprise offensive assault would be the best way to take her out, in Shalana's estimation.  Clearly Shalana was looking to betray her employer as well.
The rest of the competators have fewer useful details.  One of them is a warrior of peerless skill and height (Shalana guesses he has some giant in his heritage) raising an army on a plain on the northwest side of the island.  He also has made no progress on corrupting holy sites on the island, as far as Shalana can tell.
Conversely, there is one she calls the Ruin Diver based on a small island off the west shore of the Florensia.  He goes into the ruins alone, finds relics to give to his minions, who in turn corrupt the holy sites for him.  He's probably corrupted the most sites in Shalana's estimation.
The last noteworthy figure is a spellcaster based in the Fruited Plain on the southwestern part of the island.  She commands no willing minions.  People come to thwart her because she's a pain on cities in the area, and she either transforms them into animals that feed in the Plain, or she binds them into her service.  She says she'll free them if they obey her, but as far as Shalana can tell, she's never actually followed through on this.