From the Back of the Book:
The benevolent wizard Count Aglondier of Ilien is dead! He has left control of his realm to you, his trusted apprentice. With the considerable power of realm magic behind you, your task is to govern Ilien and defend it from those who wish to conquer your small domain.
This BIRTHRIGHT domain sourcebook is designed for players who want to take the role of the wizard king, or play a guild leader, a lieutenant, or a servant to the king.