A voice-over narrator explains that in the year 786 A.D., three large Viking ships landed in the British isles, heralding the beginning of an attempted invasion. More ships followed, and within a few years, an all-out war is instigated. King Harald, the only Viking chieftain interested in maintaining peace, makes a plea to King Loter (Franco Ressel). The English king sends Sir Rutford (Andrea Checchi), the commander of the British sea forces, to work out a deal with the Vikings. However, Rutford is not interested in making bargains, and stages a surprise attack on the Vikings, thus opening the movie. In the ensuing battle, many Vikings are killed, most of them women and children. King Harald and a few Vikings fight bravely, killing a number of English knights, but he himself is felled by an arrow fired by Rutfords chief assassin. During the battle, Harold's two young sons, Erik and Eron, are whisked away by one of his chiefs. But in the attempt to escape from the beach where the battle rages, Eron is rescued by a few Vikings along with some women and children, but Erik is left behind in the chaos.
Later, King Loter arrives on the scene where he threatens to strip Rutford of his title and of his command of the sea forces for the indiscriminate killing of Viking women and children. But Rutford retaliates by having his assassin kill Loter with an arrow, and making it seem that a wounded Viking killed him. Loter's wife, Queen Alice (Francoise Christophe), is greatly distress by the sudden death of her husband, and wonders away. She finds the young Viking boy, Erik, on the beach hiding away from where the carnage happened. Figuring out that he's a Viking, the queen decides to raise Erik as her own son, and takes him back to her castle residence, not realizing that a small tattoo on the boy's chest is a family crest which adorns the chest of both boys. Eron, in the meantime, is returned to the land of the Vikings and vows to spend the rest of his life plotting revenge against the British for the death of his father, and brother.
20 years later, the Vikings once again wage war against the British. The adult Eron (Cameron Mitchell), has fallen in love with a vestal virgin named Daya (Ellen Kessler), the identical twin sister of the vestal virgin Rama (Alice Kessler). But because of the pagan Viking custom, she is promised to the gods, and they cannot reveal their love out of fear of being executed. Eron knows that only a king is permitted to marry a vestal virgin, and so he plans to take advantage of the forthcoming war with England to prove his valor and leadership abilities.
King Olaf, the leader of the Vikings, makes a pack with Iceland, Norway, and Sweden to form an alliance to invade Britain once again for control of the North Sea. Because of his old age and physical infirmity, Olaf determins that a younger man will have to lead the attack in his place. Olaf chooses Eron, but his choice is resisted by Garan, who fears that Eron will lose sight of the objective by seeking out personal glory. Garan wishes to be elected leader, and a vote by the 20 field chieftains is taken. When the vote is a draw, Olaf determines that they will have to fight to the death. In the ensuring swordfight, Eron is victorious, but refuses to kill his opponent, and asks Garan to lead with him side-by-side. Eron is clearly a man of passion and valor, and although hot-tempered, he has compassion. But his major flaw is that Eron is too trusting.
In England, the adult Erik (Giorgio Ardisson) is appointed as Duke of Helford, and leader of the British sea forces, replacing Sir Rutford. Erik's first duty by his mother, Queen Alice, is to stave off the impending Viking invasion. But Rutford is jealous of the young man, and plots to sabotage the mission by planting a spy on board who will set fire to Eriks ship while at sea.
The two Viking and English fleets meet in the North Sea, and a sea battle begins. The Vikings board Erik's flagship, just as the spy begins to set fire to it. In the battle, Erik and Eron meet and engage in a swordfight, neither of them aware of their blood kin relationship. However, as Rutford planned, Erik's ship catches afire, enabling the Vikings to advance upon England. Erik jumps overboard, and later washes ashore in Viking land. He is found by Rama, and is immediately smitten with him, but she does not understand the significances of the cross he wears around his neck, and especially when he asks her if she's an angel. Fearing discovery and execution for interaction with a male, Rama points Erik in the direction of a local Viking fishing village and agrees to secretly meet with him later. Because of his blond, Nordic features, Erik is accepted by the Vikings as a ship-wrecked fisherman. One of Erik's crewmembers, also shipwrecked, recognizes him and plots to help him escape when the time is right.
Back in England, Sir Rutford proposes marriage to the queen. He accepts the fact that she cares nothing for him, but claims to see the marriage as an opportunity of uniting the country. However, it is apparent that he is only interested in becoming king for his own self-interest. Queen Alice immediately sees though his deception and refuses by saying. "your ambition shows. It devours you."
When the Vikings arrive, Rutford grants them admission into the castle. Eron and his men take over with little difficulty, and Rutford is appointed Regent, with the objective of ruling in Eron's absence. Eron then takes Queen Alice as a hostage back to Viking land, promising to kill her if anybody in England rebels against Rutford or his men.
In Viking land, Rama is assigned to look after the captive Queen Alice. Rama happens to notice that the queen also wears a cross, and she mentions this to Erik when they secretly meet again. Demanding to know the prisoner's name, Erik is shocked when Rama mentions that its his 'mother'. Erik surmises that his presence in Viking land is an act of fate to rescue his mother, and also find happiness with Rama.
The next day, Eron and Daya are to be married, while Rama and Erik plan to take advantage of the ensuing ceremony to flee to England with Queen Alice. As Erik, standing anonymously among all the other Vikings, watches the wedding ceremony, is mistakenly believes that it is Rama who is being married. Enraged by this imagined 'affront', Erik confronts Daya, who doesnt know who he is, and as a result, gives his true identity away when Eron recognizes him. Erik is then locked away by Eron to be executed the following morning.
After drugging the men who are guarding Erik, Rama explains to him that the woman he saw married was her twin sister, and not her. Erik is relived to hear this and escapes from his prison with Rama. However, Eron and a horde of Vikings give a pursuit. Chasing them across a rickety bridge, Eron nearly falls to his death. Encouraged by Rama, Erik, rescues Eron from certain death. Undaunted by this act of kindness, Eron continues to peruse them, but Erik and Rama, meet up with Queen Alice and they safely sail away back to England.
Upon their return, Erik is pleased to discover that the Scots have volunteered to help defend England against the Vikings. Before Erik and his combined English-Scots forces can attack the castle and reclaim it from Rutford, Eron and the Vikings arrive. Eron leaves Daya in Rutford's castle, while he accepts a direct challenge from Erik. In the ensuing swordfight, Eron catches sight of the tattoo on Erik's chest. Recognizing it as the same mark which adorns his chest, he comes to finally realize that Erik is really his long-lost brother.
Reunited with his brother, Eron declares a ceasefire. This upsets Rutford, who respons by having his henchman fire an arrow at Erik. Eron throws himself in the path of the arrow, and is fatally wounded. The enraged Vikings attempt to storm the castle, but Rutford raises the drawbridge, and promises to kill Daya by the next morning if the Vikings to not disband.
As Eron lies dying, he names Erik as his successor as King of the Vikings. Becoming more and more delirious, he asks to see Daya one last time. Erik determines to do this by breaking into the castle and retrieving her. With the help from Viking arch men, Erik begins to slowly scale a wooden tower alongside the cliff waterfront of the castle, as the Vikings shoot arrows into the wooden frame which he uses as grappling instruments. When Rama realizes that the dying Eron will not last much longer, she poses as her sister to him. Eron is oblivious to the deception, and upon declaring his love for her, he finally dies.
In the meantime, Erik has scaled the wall, and makes his way into the castle. He rescues the captive Daya, killing Rutford's henchman guarding her. At dawn, the combined Viking, English and Scots armies attack the castle. Despite heavy casualties, the Vikings succeed in scaling the walls, and fighting the defenders. Eron manages to fight his away out of the castle and lowers the drawbridge, allowing the rest of the armies to advance into the fortress. All of Rutford's men are killed with Rutford himself being the last to fall when he attempts to shoot an arrow at the escaping Eron, and he is pierced with at least a dozen arrows by the Vikings and falls off the castle rampart to his death.
With peace restored, Queen Alice reclaims her throne and allows Erik to leave England to claim his title as King of the Vikings. Erik returns to Viking land with Rama, while the dead Eron is also returned to Viking land with the mourning Daya to have a traditional Viking burial.