The Highlanders and Lowlanders are sworn enemies until Lieutenant Kemper, the son of Brigadier Kemper, the leader of the militaristic Lowlanders, is held hostage by the Highlanders until his father's army has retreated to its own boundaries. Much to his surprise, the lieutenant is treated with kindness and consideration by his captors, especially by Boyadi and his beautiful daughter Nathalia, whom he learns to love. Thus, instead of obeying his father's command to escape at an appointed time when the Lowlanders plan to violate their pledge and storm the fortress, he keeps his promise to his captors and remains a prisoner.