Born in 1150 to an aristocratic Swedish family, handsome Arn Magnusson is educated at a Cistercian monastery. As well as training to be a monk, he is to be a warrior, and becomes a master archer and swordsman under the tutelage of the giant Brother Guilbert, a former knight. But Arn is innocent in the ways of the world, and when two beautiful sisters cross his path, despite falling desperately in love with one of them, Cecilia, he is seduced by the other. Such a crime is punishable by both civil and clerical authorities, and, while Cecilia is banished to spend twenty years as a nun, Arn is sentenced to serve the same period as a Knight Templar in the Holy Land. As an occupation officer in Palestine, he discovers that the infidel Saracens don't appear to be brutish and uncivilised as they are portrayed in Christian propaganda. On the contrary, in love and war, he learns from the example of his noble adversary Saladin that there's another side to the teachings of the Cistercians...