The heroes begin as locals and outsiders caught in the first wave of the crisis. Their earliest problems are practical: missing workers, bridge issues, strange obsidian fragments in the rubble, and rumours of organised smugglers using the tunnels. Soon the investigation points south to Kridorn, where pirate-brokers and salvage crews know more than they admit, and to the sea-stack trading post of Citadel Allatro. What appears to be a local accident becomes something larger: a Darklands-connected conspiracy using the Razored Labyrinth as a surface breach.

By mid-campaign, the party leaves the river behind and ventures across the Castrovin Sea—through sea-stack mazes, submerged ruins, and lost Ninshabur. They uncover evidence of an older power beneath the Castrovin basin, one tied to the ancient cyclopean empire and perhaps even to the Spawn of Rovagug. Locathahs, merrows, Keleshite traders, and salvage engineers all hold part of the truth.

The final arc descends beneath the Razored Labyrinth into dry volcanic caverns and Darklands tunnels. The heroes must decide whether to seal the breach, sabotage the spawning chambers, or expose the conspiracy before the abyssal forces gain a permanent foothold. Victory means saving Kridorfrost and the southern Castrovin coast; failure means the sea lanes collapse, the ancient horror awakens, and the Darklands gain a road to the surface.