Everything you need to understand or teach Alamut by Judith Tarr.
The themes in Alamut are multiple but unobtrusive. Along with much medieval fantasy, it has a theme of oaths and promises. The emphasis is on the costs they extract rather than on the wickedness of breaking oaths. Aidan keeps both his oaths, to confront the Assassins and then to come back and swear fealty to the young King of Jerusalem, but the way is difficult. Morgiana, who is both his antagonist and his lover during the story's course, ultimately breaks an oath she swore to the Old Man of the Mountain. She has good and sufficient reason. He had refused her earlier plea for release, and she initially took her oath from bad motives, but her release from it too is difficult and full of danger. Joanna returns to her husband for several reasons, including her marriage vows.
It is the hardest thing she has ever had to... View more of the Alamut Summary