Bab 157: Tower of Sorcery Cleared  

It might have been more than coincidence that the ceremony of fealty between the two sisters concluded around the same time Lyghtning dealt the final blow against the Raven Queen's avatar. 

In that time, Morrigan at Twilight had kissed her sister's hand and swore an oath that Leo distinctly heard her say was, "The Vassal's Oath of Homage," which would bind her to Morgana as one of her vassals until Morgana released her from this oath. 

Now, as part of their agreement, Morgana promised to release Morrigan from her oath after a hundred years. It was either that or Morrigan would take her chances with the heroes of Adventour. 

"I am not without my own forces, as you very well know," Morrigan reminded her sister after it seemed like Morgana wasn't interested in the hundred-year deal. "I have not called upon the Night Ravens to battle yet."