Though grateful for his rescue, Sildar urged the party to focus on rescuing Gundren Rockseeker from the Cragmaw Tribe, who had taken him to their main base of operations, Cragmaw Castle. The party's first order of business was to locate the castle. Qeline Alderleaf, a halfing farmer in Phandalin, mentioned that Reidoth the druid knows the area very well, and that he was last seen heading to the Ruins of Thundertree.
The party ventured to Thundertree, where they met Reidoth in a small shack. He explained that a green dragon named Venomfang had taken up residence in the nearby tower, and that he had seen suspicious characters skulking around the other side of town. Unable to leave while Venomfang was still about, he offered to lead the party to Cragmaw Castle if they drove off the dragon.
The party scouted out the ruins, and discovered that the suspicious characters were members of the Cult of the Dragon. They were sent by their superiors to parley with Venomfang and have her join their cause. The party agreed to support the cultists during their negotiations, reasoning that if they were successful, the dragon would leave with them. Upon reaching the dragon's tower, the cultists offered the party as tribute to the dragon. Unamused by the cultists' inadequate offering, he unleashed his breath weapon on them and battle was joined. The party prevailed against Venomfang, and were able to slay the dragon before it could flee. Reidoth held true to his word and escorted the party to the castle before taking his leave.
The party scouted the castle's defenses before infiltrating it to rescue Gundren, and found a path to King Grol. The bugbear king was in the middle of intense negotiations with a drow woman, with Gundren's fate in the balance. The party ambushed Grol, his pet wolf, and the drow, defeating them along with the remaining goblins and hobgoblins in the castle. When the dark elf was slain, her form morphed into that of a gray, featureless humanoid.
After
defeating the Cragmaws, the party healed Gundren's wounds and restored
him to consciousness. He expressed his gratitude, and asked the party to
escort him to Phandalin so they could begin planning the recovery of Wave Echo Cave .