When the Mongols sack Baghdad in the year 1258, the renegade Templar Knight Rikart al-Shah'b-Rikart the Ghost-escapes the city. He tries to save two others as well-the Arab boy Daud and Dinah, the teenage daughter of a Jewish scholar-but they are separated in the chaos. Rikart and Daud make their escape separately, but Dinah is captured by the Mongols.

In the time that follows, as the Mongols continue to overwhelm Heart of the World-what a later age would call the Middle East-Rikart tries to persuade whichever Muslim or Christian leaders he encounters to unite against the invaders from the steppes. Eventually, he and Daud are reunited and together they liberate a captive Egyptian Mameluke leader whom they believe could lead the needed resistance.

Dinah, meanwhile, has been taken into the household of the wife of Hulegu Khan, brother of the Mongol emperor and leader of the Mongol army. Over time, a love affair develops between her and Nikola, one of the great khan's sons.

All of their lives will come back together at the great battle of Ain Jalut, where the Mamelukes and their allies make a desperate stand against the mighty forces from Central Asia who seek to conquer Heart of the World.