This book is written as if it were literally the memoir of the famous counter-Crusader, Salah al-Din, also just called Saladin. Also, there is a Jewish scribe in Jerusalem named Ibn Yakub, who interviews Saladin's wife and friends as part of the story.
Salah al-Din is a Kurdish military leader living in the 12th century. The city of Jerusalem has been seized by the European Crusaders. They have taken the city because of their religious beliefs about Christianity and the role of Jerusalem, but they take the city with violence, constantly regarding the Muslims who live there as heretics and enemies of God.
Then one day, Saladin arose to the task of kicking the Crusaders out of Jerusalem. He wins the city with clever strategies and good leadership, making the Kurd an instant hero in the Muslim world.
He is made the leader of Egypt and Syria. The result is continued strife over Jerusalem between the Muslims who live there and the Europeans who don't respect the value of Muslim life. Another result is that Egypt and Syria are given to Saladin, which creates political strife in those nations too. The parallel between modern Middle East politics and these ancient stories is striking.