In the year 754 AD, Frisia and Scandinavia are the only areas that have not yet been Christianized. The people who live there, known as the ‘free folk’, believe in nature gods and pagan rituals. The border lies at the Rhine River, below which  the Franks, who have been Christian for a long time, are in power. Their belief is all about culture, penance and obedience. The Franks use everything in their power, including violence, to Christianize the northern part of Europe.

When Redbad’s father, the King of Frisia, is murdered during an attack by the Franks, Redbad doesn’t feel he is worthy to step into his footsteps. Redbad's uncle makes a swift bid for power, and blames Redbad for their defeat and his father’s death. Redbad is pushed out to sea to die, but he manages to survive the journey and washes up on Viking shores, where he is slowly accepted into the clan.

When Redbad discovers his sister is being forced to convert to Christianity, to be married off to the son of the Frankish King, he can no longer turn his back. Uniting a Viking army, Redbad returns to his home soil to defend his people and battle the Lord of the Franks, Pepin of Herstal.