From the publisher's website:
The hunt for the seven shards of the Shattered Star leads the heroes back to the western coast of Varisia, to the multifaith monastery known as Windsong Abbey. The next shard of the Shattered Star appears to be hidden somewhere within the dungeons below the abbey. But when the PCs arrive, they find the monastery in ruins and held by savage giants and twisted fey! An ancient terror has returned home, and now dwells within the deep dungeons below—a terror who hopes to open the dread Doomsday Door deep within!
Beyond the Doomsday Door is a Pathfinder Roleplaying Game adventure for 10th-level characters. This volume continues the Shattered Star Adventure Path, in which players explore dungeons and wilderness in search of a powerful artifact. This volume offers an examination of the monstrous proto-demons known as qlippoth and an essay on Groteus (god of oblivion and ruins). New monsters fill the Pathfinder Bestiary, while Bill Ward's Pathfinder Journal fiction explores the seedy underbelly of the scoundrel haven of Riddleport!
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.