From the introduction:
Welcome to Scath: Shadow of the Fomori, a dark fantasy RPG heavily inspired by Celtic mythology! Welcome to a dark world where alien powers rule and humanity cowers behind flimsy walls. But there is still hope...
In this game you will take control of a Chosen One, a human whose body has merged with the powers of one of eight ancient elemental spirits. These beings have given you power. They have given you magic. But soon you will realize that such gifts always come with a price...How far are you willing to go to save your people?
This core rulebook includes everything you need to play in the world of Scath.
The first half of the book, the Player's Guide, will explain all the rules of magic, exploration and combat to you and give you information both about the Chosen Ones and the crumbling, desperate human societies they come from.
The second half, the Gamemaster's Guide, includes rules for many terrible monsters and their mystical masters, the Fomori. It also gives you detailed information about the lands of Scath and the legendary characters that live in them. Finally it includes rules for pitched battles, when the Chosen Ones have gathered the forces of humanity behind them and are leading them to one all deciding war against the Fomori.