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!