Specters of Yorgen Reef

Our heroes arrived in Immsdamme at the behest of Gthoras, one of Sevonia's old buddies. However, the man is nowhere to be found, though they do encounter Backmynster Bredswed also known as Backy. Backy runs the general store and was a business partner of Gthoras before he mysteriously disappeared a week or two ago.
The heroes decide to remain in town and investigate the weirdness that is going on. On their search for Gthoras, they are watched by some strange, fishlike beings who disappear into the waters of Ivan's Bay. However, this does not discourage them. They seek out the local hermit drunkard who resides on the north edge of town, who spills the beans shortly before almost succumbing to a drug in the wine. The hermit explains that the manor atop the hill which overlooks the rest of the town is said to be tied to the history of the town. In the cellar of the manor they find a similar fishlike creature, though this one seems to possess eldritch powers, capable of bending space. He also talks of how there are lights out on Melik's Waters.
Following a lead acquired in the manor, but mostly a hunch, they investigate the temple. It turns out the priests are part of a cult that is abducting, controlling, and altering people. Armed with this knowledge, they arm an assault upon Yorgen Reef, the base of this cult. After finding their way through a dark cavern, and a settlement of presumable fish people, they arrive at an underground temple. Using a magical disguise, they are able to fool the guards into letting them inside. Once they get stuck at a secret passageway however, they dispatch most of the guards and take one hostage to lead them through the temple.
Braving the challenges within, they make their way to a chapel suspended over a precipice. Inside they find Hylde, who summons his Firstborn, a creature of horrible eldritch appearance and power. It is only by the skin of their teeth that the heroes manage to triumph and release the prisoners held in cages, hanging from the chapel. All the transformed townsfolk go insane, while the party finds the man they were looking for at the docks contemplating his situation.
With the reef cleared of evil magic, they return to Immsdamme, very tired, almost dead, and incredibly hungry.