Arn's brothers wold be-fiancee fails to seduce Arn before he finds out she's the sister of his beloved. Prince Knut, now an adult, is back from Norwegian exile to reclaim the throne. He lures crack archer Arn to help him kill the usurper, but Arn's family fears that only leads to civil war. Arn's siren convinces the bishop that her alleged lover Arn and his true love, her sister, committed mortal sins, so they are confined to strict convents for 'half their lives', 20 years. Arn's abbot however gets his sentence commuted into joining the Knights Templars, a crusading order.