The ruins of the Great City of Pnaktous await! The investigators have learned that the cult of the Crawling Chaos is excavating the ancient city for reasons unknowable, but to thwart the cult, the heroes will chase them to the ends of the earth. Exploring the depths of this inhuman city is not without its own dangers, aside from the cultists. Strange artifacts, hazardous ruins, and terrifying monsters lurking in the darkness. Perhaps the team will find aid in the most likely of allies though...