From publisher blurb:
In The Viperian Curse, a level-4 Shadowdark adventure, a terrible illness has fallen on the townsfolk at Pink-Apple Village. Those afflicted grow weak and their skin turns brittle and scaly, like a reptile's. The locals have had a centuries-long quarrel with a covenant of viperians, serpent-folk. They are certain that the viperians are guilty of the disease but don't know where they hide.
The characters must visit an ancient elvish crypt where a spirit is their only hope to reveal the location of the viperians' lair. In the House of Serpents, the characters fight fiercely to stop the snake-folk leader and interrupt their foul chanting ritual. Alas, the characters shall awake the true rage of the viperian bloodline.
This Shadowdark adventure has the heroes interact with an elvish ghost that collects a ruinous price for his service, has them explore an ancient viperian structure, and gives them the chance to save a community from certain death.