After Jarl Borg's death, an ally of his swears vengeance on Ragnar. While Ragnar is away raiding, this man seizes Kattegat and leaves his son in charge. What follows is a nightmarish experience for Bjorn and Porunn; who find themselves and their love tested by their harsh treatment. What's more, with the invaders expecting him, Ragnar will find it difficult to return to save them.