The story is set in the 10th century and follows Ahmad, who is sent as a diplomatic envoy from the Abbasid Caliphate to the northern lands. When his journey takes him to a Viking village, he finds himself caught in a deadly conflict. The Vikings are preparing to defend their land from an eerie, almost supernatural enemy known as the Wendol—an ancient, barbaric tribe that preys on the villagers. Ahmad, initially an outsider and ill-prepared for the rough life of a Viking warrior, is reluctantly brought into their fold as the 13th member of their fighting force. His inclusion in the group is crucial, as the Vikings believe that having 13 warriors is essential for their survival.

Despite being unfamiliar with their brutal customs and warrior culture, Ahmad proves his worth over time as he learns to fight, adapt, and bond with the group. As they travel to confront the Wendol, Ahmad and his comrades face not only physical battles but also a war of belief and identity. As an outsider, Ahmad initially struggles to understand the pagan Norse traditions, but as the story unfolds, he grows to understand the Vikings’ sense of brotherhood, loyalty, and the importance of facing their enemies with courage.