Thundertree Cultists

After returning Gundren Rockeeker to Phandalin, the trio are approached by Qelline and her longtime friend, Reidoth the Druid. The druid Reidoth visits Thundertree from time to time, keeping a wary eye on its dangers. He explains that thirty years ago he eruption of Mount Hotenow devastated Thundertree and a subsequent plague of strange zombies swept over the area, killing or driving off those who survived the eruption. Though most of the zombies have long since crumbled to dust, strange magic permeating the area has mutated the local vegetation into new and dangerous forms. He asks the trio to investigate further.
 
It was then the trio met Barry, a dragonborn paladin, who was on a holy quests and wished to partake in the investigation. The three adventurers obliged and they set off to Thundertree.
 
While in Thundertree, the group came upon some cultists, and while battling them, one turned on his compatriots and revealed himself to be Arvard, a human swordsman, who has been infiltrating the dragon cultists in the hopes of destroying them. He joins the adventurers in their quests to cleanse the area. Arvard tells the group that the cultists are called the Cult of the Dragon. They have located a black dragon in the surrounding area and have been worshipping it from afar.
 
The adventurers fight off the cultists and slay the dragon, ridding the area of the strange magical curse that has plagued the ruins of Thundertree.
 
Arvard and Barry join the adventurers in returning to Phandalin for rest.