"Shadowsfall: Temple of Orcus" is the 2012 Free RPG Day adventure from Jon Brazer Enterprises. It's a pathfinder compatible product.
From the back of the book:
Fight the Dark Side
For the game master, a new plane of peril - Shadowsfall. This Level 5 Adventure takes your gaming party to the Plane of Shadows. The head of the local militia and her children are missing and only the characters can rescue them. In this introduction to Shadowsfall, challenge your adventurers to brave the Land of Eternal Night.
For the avid player, four sample 5th level characters showcase new player options for the Shadowsfall setting - a dhampir champion of innocents, a former angel seeking arcane secrets and a lost love, a bomb-toting kobold native to Shadow, and a fetchling profiteer from the zombie slave trade ready for play in your campaign.
Designed to enhance your world and your game, this expansion supplies a one-page overview of Shadowsfall and features distinctive monsters of Shadow created for the Book of Beasts: Monsters of the Shadow Plane - the newest in award-winning series available at your game store today.