Heroes: Aelarion, Broil, Oculor, Sengar.
Following up on the letter they found in the Old Observatory, the Heroes visit the mine manager Balabar Smenk, who confesses he's been "bullied" into helping fellow mine-manager Ragnolin Dourstone and the Ebon Triad, a dreadful cult bound to create the Overgod, a merging of the three evil gods Hextor, Vecna, and Erythnul. Balabar now fears for his life, and suggest the Heroes take care of the cult and of Ragnolin.
The Heroes inflitrate the Dourstone mines, descending into the lower levels thanks to an elevator. They find themselves into a Dark Cathedral, guarded by Tiefling guards devoted to Hextor. The Heroes defeat the guards, and set forth to explore the compound.
The Dark Cathedral gives access to three different compounds, each of them dedicated to one of the dark gods (Hextor, Vecna, and Erythnul). The Heroes begin with the exploration of the Temple of Hextor, and must contend with skeleton guardians and crazed cultists.