From back cover:

The adventures in The Night of Dissolution pit the player characters against the darkest forces the city of Ptolus has ever faced. Following the threads of a hidden conspiracy, the characters find themselves up against insane cultists, wild chaos magic, and horrors from the primordial days of the world.

The urban intrigue, dungeon exploration, and high action take PCs to a former brothel, the laboratory of the dreaded Surgeon in the Shadows, and even secret temples of chaos. It all culminates as the characters attempt to stave off the Night of Dissolution: a dark time long foretold when the slumbering Lords of Chaos will awaken in their hidden lairs deep below the city—and bring catastrophe to the world.