A grim ritual, already in progress, will use the power of the Serpent's Skull to restore the serpentfolk of Golarion to their true, terrible potential, instantly creating a new menace below all the nations of the world. A lost Pathfinder holds the key to disrupting the ritual, but before his plan can be executed he must first be rescued from his underground prison. A Pathfinder Roleplaying Game adventure for 13th-level characters, this volume continues the highly anticipated Serpent's Skull Adventure Path, in which the heroes fight their way through a treacherous jungle to discover and plunder an ancient lost city. This volume contains a wide-ranging gazetteer of the serpentfolk city of Ilmurea, with tips for expanding the location to enrich the campaign. An overview of Nethys, god of magic, by Sean K Reynolds, provides new insight on one of Golarion's most important deities. Plus five new monsters in the Pathfinder Bestiary, new fiction in the Pathfinder Journal, and much more!