The story takes place in 12th century Sweden where two mighty families fight over crown and power. Arn Magnusson (Joakim Nätterqvist) is the young heir of the Folkunga family who is sent to the fighting grounds in the Holy Land as a penalty for having a forbidden romance with beautiful Cecilia (Sofia Helin), whose father leads the rivalling clan. As the knights embark on a dangerous journey towards the Middle East, Arn soon proves his courage and fighting skills to all disbelievers. Meanwhile Cecilia is been held almost like a prisoner in a distant monastery, anxiously waiting if Arn will ever return and set her free.