On the trail of a powerful ancient enemy, the adventurers seek more information in a merfolk city teeming with intrigue just beneath the waves. They arrive in the free city around the same time that a group of deep merfolk came to the city claiming that the place is in the path of a destructive sea monster. This warning is nothing more than a ruse for the campaign's villain to uncover the location to a secret Azlanti military laboratory that contains a dangerous weapon. The adventurers must carefully maneuver the social currents of the underwater city and unravel dangerous intrigue to get to the bottom of the merfolk's plot and discover where the ancient enemy is headed so they can stop it.

"City in the Deep" is a Pathfinder Roleplaying Game adventure for 10th-level characters. The adventure continues the Ruins of Azlant Adventure Path, a deep dive into aquatic adventure. A selection of new monsters, a gazetteer of a submerged city, and an ecology of merfolk round out this volume of the Pathfinder Adventure Path.

Each monthly full-color softcover Pathfinder Adventure Path volume contains an in-depth adventure scenario, stats for several new monsters, and support articles meant to give Game Masters additional material to expand their campaign. Pathfinder Adventure Path volumes use the Open Game License and work with both the Pathfinder RPG and the world's oldest fantasy RPG.