Joscelin was the ... son of a great warrior. His mother died during his childhood and took his father's heart with her to the grave. Because his father has legitimate heirs, Joscelin had few prospects. He had run away from home to fight as a mercenary at the age of 15. Seven years later he had returned as the captain of his own troupe. Since then he had taken service where it was available and when it wasn't available he had rode the tourney circuit. Now he has returned home briefly before beginning employment with the Justiciar of England, who ruled while King Henry II was in France.
On his way home he encountered Linnet and her husband. Married at 13 to a brutal Lord, Linnet had one son she cherished and tried to protect from her husband's brutality. She suspects her husband is plotting treason. She knows that her husband is destroying her son's inheritance in futherance of his plans.
While the political background is important, the real driving force in this case is the dynamics set in force by Joscelin's father decades before.