As the adventurers work to track down the missing colonists, the trail leads to a nearby island. There, the adventurers discover the submerged ruins of a cathedral dedicated to a now-dead god that has become a lair of an ichthyic monster and its cunning minions. The adventurers must fight their way through flooded chambers and vicious monsters to find the kidnapped colonists and learn the greater threat to the region and to humanity as a whole.

The Flooded Cathedral is a Pathfinder Roleplaying Game adventure for 7th-level characters. The adventure continues the Ruins of Azlant Adventure Path, a delve into the lost past of humanity's first empire. Several new monsters, a look into the gods of ancient Azlant, and more information about the complicated construction of clockworks round out this volume of the Pathfinder Adventure Path.