Wretched

From publisher blurb:

An adventure for expert characters

Something dwells in the reeking swamp near the village of Fimmoran. The locals say it’s a witch who has cursed their children with an unnatural disease. The people of Fimmoran want the crone’s head and are willing to pay for it. There is a twist in this black-hearted tale, though—a twist the characters will discover when they venture into the swamp. The adventure ends when the characters determine the true cause of the children’s sickness and deal with the repercussions of that discovery.