Seeking Dorn

Upon our return to the seas off Barsella, we realized that a few of our party on board the Spotted Fin were sick with this plague: Eagungad, Nova, Riston, and Bigby (Riston's familiar). Therefore our need to seek out Dorn is even more dire! Evain takes us to the Burning Shores, despite our ship being trailed at times by the Barsella navy - they must be aware of our breaking the quarantine!
 
On the way we learn more of this Alastair Dorn: he is a powerful wizard from the Mage Wars [which interests me, I must confess! He and I may be the only living survivors of this time.] This makes him over 400 years old (good lord, what is my age, then?). We safely arrive on the Burning Shores, and discover Dorn's tower atop these obsidian cliffs, accessible by one rickety elevator lift. As we elevate up towards the top of this cliff, we are attacked by two Mephits - those fire-spitting bastards.
 
Regardless, we make it to the top and see Dorn's tower, which is surrounded by twenty-one doors! We choose one to go in, and find Dorn's library. Reading the books and documents there, we learn some important information: notably, the plague is NOT natural, and is not of this plane. Rather, a mystical ritual started this illness, and there is a clear PATIENT ZERO. Removing this ur-patient will slow the spread of the disease, which appears to originate from the realm of the Great Old Ones.
 
There is a blackboard in Dorn's tower with text written in Void Speech, that I am able to decipher: it refers to a summoner Maximilian Song on his deathbed; Harrow discovered leave to home plane. (?) Harrow appeared over a century ago, and may be an angel?
 
As we attempt to leave the tower, the door we came through leads us under water (thank god we had Potions of Breathing and I had the Scavenger's Ring my party found in the north!). As we emerge from this terrifying underwater ordeal, we find ourselves in a well, in Flotsam Village, an island of Malka that sits in the center of the Aroan Triangle, where lost sailors arrive randomly and where we find an open throne that is believed to serve as Harrow's temple? Harrow usually escorts new arrivals - he was gone when we arrived, last seen twelve days ago.