From publisher blurb:
In Living on a Prayer, a group of level-6 adventurers learns about Arthur Stevens, a priest. Wishing to belie myths about a shunned location, the well-loved priest gathered twenty followers and delved inside the ancient temple. In the outskirts of the city, the House of the Obsidian Masks remains uncharted and avoided. But Arthur and his entourage believed the rumors were nothing but superstitions and exaggerated lies.
How they were wrong... D'rezzit, the demon that forced the elves that built this place to abandon it, is the source of all those rumors and stories. The poor priest fell to the temptation of the soothing, sweet, words from the demon, who impersonated the man's deity through a giant mask. Thus, the Obsidian Cult was born, and the city has never been more endangered.