Thorfinn, a boy living in Iceland, longs for adventure and is eager to know more about the world. He dreams of a land of paradise called Vinland that he hears about from the adventurer Leif, while he leads his peaceful life with this father Thors, a former warrior. One day, Thors saves a runaway slave and sets a series of events in motion. This is the story of a true warrior in an age of turmoil.

In the year 1002, the war between England and Denmark was intensifying. One day, the Jomsvikings pay a visit to Thorfinn's village in order to bring back Thors, their former commander, to prepare for the impending battle. Thors is forced to join the war in order to protect the villagers from being taken hostage, and must face his accursed past in order to save his family and his village.

Askeladd, the leader of a Viking army of a hundred men, receives orders from Floki of the Jomsvikings to kill Thors, who was once known as the Troll of Jom. However, the villagers, completely unaware of the order, buzz with excitement as they prepare for their first battle. Thorfinn also joins in the excitement. Thors and his men are about to embark on a difficult sea journey to England.

Thors and his men fall for Askeladd's trap and faces a dangerous situation, but Thors defeats many of Askeladd's men with his overpowering strength. However, Thors knows that it will be difficult to save everyone, including his son, who've been living in a peaceful village their entire lives, and makes a tough decision.

After Askeladd kills Thorfinn's father Thors, Thorfinn hides inside Thor's ship and bides his time until the opportunity to take revenge. However, life on the ship is harsh without any food or water, and Thorfinn grows weaker day by day. One day, Thorfinn, armed with his sword, attempt to attack Askeladd in his sleep...

Thorfinn kills his first man. As more time goes on Thorfinn kills more men and becomes more skilled. One day when Thorfinn is in battle he gets shot with an arrow and ends up unconscious. An English woman and her daughter help him recover.

Askeladd withdraws temporarily from the war against England. While searching for a new source of income, he encounters a skirmish among the Franks and hatches a plot to steal their treasure. Askeladd sends 16 years old Thorfinn, who has grown up into a cold-hearted Viking, ahead as a messenger.

After capturing the treasure from the Franks, Askeladd's men return to the village of Gorm on the Jutland Peninsula in Denmark to pass the winter. Thorfinn challenges Askeladd to a duel as a reward for bringing him the head of the captain of the clan of Franks. Even though Thorfinn has grown in skill through his experience in battle, he is still no match for Askeladd.

In October 1013, King Sweyn leads a fleet of Danish and Viking ships in an attempt to take London Bridge of England. Askeladd's army, hired by the army of Denmark, was among them. However, after the betrayal of Thorkell the Tall, a Viking known for his overpowering strength, London Bridge has become impregnable. Askeladd tells Thorfinn he'll reward him with a duel if he's able to kill Thorkell.

Askeladd's army separates from the army of Denmark and attacks a village 100 km to the west. Thorfinn leaves the soldiers behind in disgust and climbs up a hill overlooking the village, where he pledges revenge for his father. However, he encounters Askeladd sitting in the darkness, who tells him about "Britannia", the aging of the world, and Ragnarok, the final battle.

Thorkell takes Canute hostage and follows after the main army of Denmark. Ragnar objects to Thorkell’s plan to take on the entire army of Denmark, boasting 16,000 soldiers, with only 500 men. Thorkell then begins to tell Ragnar the story of Valhalla, the pride of Normans, a place where only those who die in battle can go.

Askeladd and his men continue their march to escape from Thorkell. However, their march comes to a halt at the Severn River. Askeladd hands a letter to an old man operating a ferry across the river and tells him to deliver the letter to the other side immediately. As soon as he hears the addressee’s name, the old man sets off in his boat.

Askeladd crosses the river and escapes from Thorkell into Wales with Canute. However, Askeladd’s men are ambushed by a group of soldiers hiding behind the boulders at the border of the kingdom of Brycheiniog. Askeladd attempts to negotiate with their messenger and reveals his plan.

Askeladd and his men change course and decide to return to Gainsborough, by crossing through the Earldom of Mercia in the midst of a harsh snowstorm, where the main army of Denmark awaits. The men spot a small village in the blizzard and make their move.

After losing Canute, Thorkell decides to halt his advance in central England. Thorkell hears that the end of the war between Denmark and England is near, and bemoans the end of the war. However, he later gets wind of an interesting piece of news.

Askeladd and his men are attacked by the English army in the village where they had planned to camp during the winter. Askeladd captures their captain and interrogates him to find out how the English knew where they were, and discovers that Thorkell is fast approaching. The news of Thorkell's arrival sends waves of shock among Askeladd's followers.

Askeladd's men continued their march to escape Thorkell. However, Torgrim and his friends were hatching a plot to switch sides and join Thorkell, taking Canute with them. Torgrim finally launches his rebellion and corners Askeladd, negotiating with him to hand over Canute, then Thorkell arrives in the midst of the confusion.

Thorfinn and Thorkell agree to have a duel over the fate of Askeladd. Thorkell looks forward to facing off against Thors’s son, Thorfinn, and asks him what a true warrior really is. Meanwhile, Canute is suddenly ambushed while he attempts to escape, and has a dream about a certain individual.

Thorfinn suffers a serious injury in his fight against Thorkell. Thorfinn is told to think about what he has to do to beat Thorkell. Askeladd treats Thorfinn’s wounds so that he may fight again someday, and proposes a joint strategy to help the two of them survive longer.

After the fighting dies down, Canute takes in Askeladd and Thorkell as his followers, and returns to Gainsborough. Canute goes through an awakening when he realizes the meaning of love in the aftermath of Ragnar’s death. Canute throws away what little feelings he had left for his father, and joins Askeladd in plotting to assassinate King Sweyn.

Canute’s party arrives in York to attend the Imperial Council. Although Canute had wanted to strike out against King Sweyn, the King was being guarded by the most powerful Jomsviking unit in the Northern Sea while keeping a close eye on Canute. With the situation strained to the breaking point, Askeladd comes up with a plan. Meanwhile, Thorfinn is reunited with a person who knew his former self.

Thorfinn begins his duel against Askeladd with Canute and Thorkell as witnesses. However, Thorfinn is unable to strike as he stands overwhelmed by the extraordinary mood that overtakes Askeladd after Bjorn's departure. Having noticed Thorfinn's hesitation, Askeladd lays down his sword and provokes Thorfinn into an unarmed fight, which incites Thorfinn's fury.

After the assassination attempt on Canute’s life, rumors spread through York saying that the king is trying to kill Canute. As a result, the king is unable to issue any orders that would put Canute in harm, and Askeladd is pleased that everything is proceeding as planned. However, the tables turn when King Sweyn speaks. Meanwhile, Thorfinn is sent to prison as punishment for disturbing the peace.

Askeladd comes forth before King Sweyn and implores him to halt his invasion of Wales. Meanwhile, Thorfinn decides to return home at Leif’s urging. However, the moment before he boards the ship, Thorfinn catches a glimpse of a single tern taking off into the sky...