King Bagsecg (James Cosmo) of the Vikings, leads his weakened army against the Saxons in 871 AD. As the violence escalates, Bagsecg's calls for re-enforcement, including his son Prince Steinar (Charlie Bewley). Steinar travels with a small band of trusted soldiers including Hagen (Clive Standen), Grim (Michael Jibson) & Jokul (Guy Flanagan). Steinar reaches his father only to find that the army was defeated in a battle & his father Bagsecg badly wounded. Steinar wants himself to be proclaimed king, but Bagsecg asks Steinar to find Hakan (Elliot Cowan), Bagsecg's first born, a man who Bagsecg believes is worthy of becoming king. Bagsecg did not find Steinar's elder brother worthy of the crown. Bagsecg also wanted Steinar to kill Vali, Bagsecg's stepson, who refused to pick arms in battle. But Steinar refuses to murder his half-brother. Hakan was banished by Bagsecg himself for being insane, but Bagsecg claims that the time has passed now. It is time for Hakan to return home.The group decides to search for Hakan together & to find Hakan they must find Ivar (Ivan Kaye) who resides in the black mountains. Hakan and Ivar used to hunt together. When Hakan was banished, Ivar was not tolerated either, and he went looking for Hakan. However, Steinar's elder brother Harald (Finlay Robertson) is angry at the decision & when Steinar leaves, he goes to meet the Saxon king & makes a deal with them to become King of Vikings when Bagsecg is dead. This news is brought to Steinar by Vali (Theo Barklem-Biggs), the stepson of Begsecg. Steinar allows Vali to ride with him in search of Ivar, as it was too dangerous to leave him with Harald, who wanted to kill Vali as per Bagsecg's wishes.Steinar wonders why Bagsecg banished Hakan and now wants to make him King. They leave Vali with their horses at the edge of the Black Mountains & enter the Mountains & find Ivar. Steinar defeats Ivar in a game of arm wrestling & in return Ivar agrees to take them to Hakan. Ivar brings along his slave Agnes (Alexandra Dowling) for the journey. When the group returns to Vali, they find all the horses dead, which Vali says is the work of thieves, but not a scratch on him.Further on, the group is attacked by a well-trained company of Saxons & Grim dies while battling them. Later Hagen finds a Saxon coin dropped by Vali & thinks that Vali might be leaving markings behind for their enemies to follow, which is how the Saxons were able to ambush them. Steinar knows that if Harald made a deal with the Saxon King, then killing Steinar would be part of the deal. Steinar refuses to believe that Vali betrayed him, as his mother is also a Saxon. But as they are debating this, the group is again attacked by the Saxons & this time the Saxons capture them.Saxon's leader tries to interrogate Steinar, but the Saxons don't kill the Vikings. The Saxon leader offers to make Steinar the leader of his people, in exchange for an alliance between the Saxons and Vikings and the Vikings acceptance of the Church. Steinar is rescued by Agnes, who had escaped by hiding when the Saxons attacked. Steinar in turn rescues the rest of his team. Ivar dies from his multiple wounds but points Steinar in the direction where he can find Hakan.Hagen locks up the captured Saxons in a nearby church and burns down the entire building. Hagen & Jokul plead with Steinar to kill Vali so that the Gods will look favorably on them for the rest of their journey, but once again Steinar refuses. Hagen fights Steinar & eventually Steinar kills Hagen.The journey continues & Steinar eventually reaches the forest which Ivar pointed him to. He finds Hakan in a cave ruling over a group of savages & nothing more than a savage himself. Hakan kills & eats Jokul & kills Vali by gouging his eyes out. Steinar learns that Hakan was banished by Bagsecg as Hakan & his own mother started a carnal relationship. Hakan and Steinar's mother was living in Hakan's cave as his lover. Hakan demands that Steinar bows to his commands, but Steinar refuses, so Hakan challenges him to a fight to the death.Steinar defeats Hakan & cuts his head off. He takes Agnes & Hakan's head back to Bagsecg. Steinar kills Harald, becomes the King of Vikings & leads them on the battlefield against the Saxons.