In mid-eighth-century Europe, Norse Viking chieftain Ragnar invades the English territory of Northumbria, killing its king, Edwin, and raping Queen Enid. Two months later, when Edwin's cousin Aella ascends the throne, Enid confides in Father Godwin that she is pregnant with Ragnar's child. Father Godwin offers Enid sanctuary and after her son is born, arranges to move the infant to Italy where he can grow up safe from Aella. Enid agrees and leaves her son with only a necklace containing a royal stone to identify him. Twenty years later after Enid's death, Aella prepares to marry the young Welsh princess Morgana, hoping that the combined forces of both countries will halt the continuous Viking raids. Enid's cousin Egbert has long been aware of the existence of her illegitimate child and believing that Aella is unfit to rule, has been secretly in league with Ragnar to help overthrow Aella. When the suspicious Aella accuses Egbert of treason, Egbert is forced to accept protection from Ragnar in the Northlands. Upon arriving at Ragnar's lair, Egbert meets Ragnar's brash son Einar who is displeased by the arrival of the Englishman. Later, showing off his trained hawk to Egbert, Einar is startled, then angered when another hawk interferes and captures the prey. Discovering that the other hawk's owner is a slave, Eric, Einar accuses him of having stolen the bird. In a fury, Eric orders his hawk to attack Einar, whose eye is gouged out. Although stunned, Einar orders that Eric be held until that evening's feast when he will pronounce judgment on the slave. At the bawdy evening festivities, however, the tribal mystic Kitala foretells that the Viking god Odin will curse anyone who kills Eric. Scoffing at Kitala's prediction, Einar and Ragner decide to have Eric placed in a tide pool filled with aggressive crabs which will bite him until the tide drowns him. As Eric is lead away, Egbert is startled to recognize the strange stone around his neck that identifies him as Enid's son and Einar's half brother. Later, Egbert joins Kitala at the tide pool where Eric has been imprisoned and learns that Eric was captured in a Viking raid as an infant and brought to the Northlands to become a slave. While Kitala prays to Odin, a sudden wind shift drastically lowers the tide and Egbert frees Eric, claiming him as his own slave. When Einar protests, Egbert threatens to stop drawing the maps vital for Ragner's raids on Northumbria unless he is allowed to keep Eric as his slave. Egbert then advises Ragnar of Aella's plans to marry Morgana and suggests that kidnapping her would upset the king's retaliatory scheme against the Vikings. Einar agrees and sails to intercept Morgana en route to Northumbria. Meanwhile, Kitala and the mute, former slave Sandpiper present Eric with a gift of a fish carved from an enchanted metal that always points to the north. When Kitala predicts that Eric is destined for greatness with the help of a woman, Eric laments that he will likely remain a slave forever. Out at sea, Einar successfully stops Morgana's ship and takes her and her maid Bridget captive. Einar is attracted to Morgana's youth and beauty, but his advisors remind him that the princess must retain her honor in order to bring a substantial ransom from Aella. Eric is dismayed by Einar's victorious return to the Northlands, but taken by the sight of Morgana. That night, Ragnar throws a welcoming feast for his son and declares Morgana now belongs to Einar. Drunkenly pleased, Einar visits Morgana but is dismayed when she unconditionally refuses him. As Einar is about to attack Morgana, Eric breaks in and knocks Einar out, then offers to take Morgana and Bridget with him, Kitala and Sandpiper on a small boat that they have stolen. Soon after, as Eric forces the princess and her maid to help row at sea, Einar revives and, joined by Ragnar, sets sail in two ships to pursue Eric. Using the metal fish as a guide, Eric steers the boat through dense fog, avoiding the rough coastal reefs. Meanwhile, Ragnar's ship crashes against the reefs and is sunk. Eric rescues Ragnar, but Einar, believing his father dead, vows revenge against Eric. The following day, Eric tells Morgana of his feelings for her, but she insists that she is pledged to Aella. When Eric offers to take her to Aella to ask for a release from her pledge, Morgana agrees. Back in Northumbria, Eric offers to turn over Ragnar to Aella in exchange for Aella releasing Morgana from her pledge. Aella is incensed when the princess agrees with the proposal. Placed in a cell for breaking her pledge, Morgana is later visited by Father Godwin, who is startled to discover her wearing the royal stone necklace, given to her by Eric. While Father Godwin tells Morgana of Eric's birth, Aella orders Ragnar to be thrown into a pit of wild wolves and demands that Eric push the Viking into the pit. When Ragnar asks for a sword in order to die with honor, Eric complies, enraging Aella. After Ragner leaps into the pit to his death, Aella threatens to kill Eric for his defiance, until Morgana then intervenes, promising to adhere to their marriage pledge. Aella accepts, but cuts off Eric's left hand in punishment before setting him adrift in his small boat. Some days later in the Northlands, Einar tries to rouse the men to resume their search for Eric, but the men fear that Eric is protected by witchcraft. As a despondent Einar prays alone to Odin, he is shocked by the arrival of Eric, who demands a ship to return to Northumbria to save Morgana. After Eric details Ragnar's honorable death and his punishment for defying Aella, the other men heartily agree to avenge Ragnar and Einar promises to spare Eric until Morgana has been rescued. Along with Egbert, the Vikings sail against Northumbria where Einar and Eric lead the fierce assault against Aella's heavily fortified castle. After breaking into the castle, Eric goes in search of Aella and Einar seeks out Morgana, whom Father Godwin has sheltered in the chapel. When Eric finds Aella he throws him into the pits of wolves. Einar discovers Morgana in the chapel but when she insists that she loves Eric, Einar demands to fight for her. In his angry frustration Einar ignores Morgana and Father Godwin's revelation that he and Eric are half brothers and seeks out Eric for a confrontation. After a long, drawn-out sword fight with Eric, Einar abruptly hesitates and is run through by Eric. Puzzled by Einar's action, Eric nevertheless places a sword in Einar's hand as he dies, ensuring his admittance into the hero's Valhalla. Later, Eric and Morgana, who plan to bring together Northumbria and the Northlands in peace, provide a traditional Viking funeral for Einar.
