In the time of King Arthur, a group of Vikings led by Sligon betray the Christian king of Scandia, Aguar, and steal his throne, which forces him to flee to Britain. With his wife and impetuous, athletic son Valiant, Aguar lives in a secluded abbey, the location of which is known only to Arthur and Boltar, Aguar’s closest friend. One day, Boltar arrives with news that Sligon is intensifying his efforts to find the exiles, and so Aguar orders Valiant to travel to King Athur’s court at Camelot and become a Knight of the Round Table. During the journey, Valiant spies upon a knight dressed in black armor as he meets with a group of Viking warriors. The Vikings promise the Black Knight that if he delivers the exiles, Sligon will send him 1,000 armed men, but their parlay is interrupted when Valiant falls from the cliff onto the beach where they are meeting. Valiant steals the horse of the Black Knight’s squire and escapes, then, when he hears another rider coming, knocks the man off his horse for fear that he is allied with the Black Knight. The rider quickly overpowers the youth and reveals that he is Sir Gawain, whom Aguar had told Valiant to trust. When Valiant informs Gawain of what he has seen, the knight takes him to Camelot, where Valiant relates his story to Arthur. Many of the knights at the table are skeptical of Valiant’s tale, as the Black Knight is considered a non-existent phantom, but the grateful Arthur offers Valiant a reward. Valiant asks to be knighted, to which Arthur replies that he must first become a squire and earn his knighthood. Although the erudite Sir Brack, Arthur’s illegitimate brother, offers to train Valiant, Arthur offers the Viking to Gawain, and Gawain cheerfully begins instructing him in the use of the joust, axe and sword. One day, Brack announces that he is going to search for the Black Knight, and Valiant sneaks away to help. Although Aguar had cautioned Valiant not to tell anyone their location, Brack is able to deduce where Valiant came from when he shows him where he saw the Black Knight. Brack then tells Valiant to wait alone while he investigates farther afield, and Valiant is set upon by a dozen archers. Valiant is shot in the back as he escapes, and after falling from his horse, crawls to a lake, where sisters Aleta and Ilene are bathing. They take him to their home, where their father, King Luke of Ord, grows disgruntled by the amount of time Aleta spends nursing the Viking back to health. Luke, who wants Aleta to marry Brack, orders her to stay away from Valiant, but by the time Valiant is able to walk, the young couple has fallen in love. Brack, who desires Aleta, arrives and claims that he had searched for Valiant but could not find him until now. When Brack decides that Valiant is well enough to return to Camelot, Aleta, desperate to spend time with her sweetheart, suggests that the family accompany them to attend the yearly tournament. Upon arriving at Camelot, Valiant learns that Gawain, while searching for him, was seriously injured by the same archers who attacked him. Valiant pleads with Gawain to forgive his earlier desertion, and the gruff knight agrees, although he sternly disputes Valiant’s theory that Brack is the Black Knight. Valiant then introduces Gawain to Ilene, who has been infatuated with the knight for years without his knowledge, and rushes to find Aleta. Aleta enters Gawain’s chamber alone, and after falling in love with her at first sight, Gawain mistakenly believes that Ilene is Valiant’s sweetheart. Valiant, who has been warned that Gawain is more seriously injured than he believes, does not have the heart to correct his hero’s mistake, and so avoids Aleta for the next three days. Aleta assumes that Valiant does not really love her, and on the day of the tournament, confronts him. Valiant refuses to speak in his defense, and after tearing off the cross he gave her, Aleta joins her father. Luke announces that the winner of the tournament will receive Aleta’s hand in marriage, and Aleta watches in horror as Brack easily clears the field of his opponents during the jousting. It appears that Brack will win until suddenly Gawain appears, but after Brack unseats him, his helmet is removed and the onlookers gasp as Valiant is revealed. The disgraced squire is hurried off the field, while another challenger appears and succeeds in defeating Brack. The challenger is revealed to be the real Gawain, who collapses after his victory. In his tent, Brack receives word that Aguar and his queen have been captured and is given Aguar’s ring, which Aguar had promised to send to Valiant if he was needed. When Valiant is brought before Arthur for the crime of impersonating a knight, Brack arranges for him to be confined to quarters while awaiting Gawain’s recovery. Valiant pledges not to flee, but when Brack later tosses the ring into his room, Valiant is forced to leave. Aleta sees Valiant preparing his horse, and after begging him not to break his vow to Arthur, swears her undying love. As Valiant is journeying to his home, he is attacked by the Black Knight and his men, who are then met by their Viking cohorts. Valiant is not surprised when Brack reveals himself to be the traitorous knight, but is infuriated to learn that his parents have already been captured, and that Brack intends to dethrone Arthur. Aleta, who has followed Valiant, is also captured, and the couple are taken to Scandia, where Valiant refuses to tell Sligon the names of other Christian Vikings. While Valiant and Aleta are taken to the dungeon, Boltar meets with other loyal Vikings and urges them to take action, even though they are outnumbered. Boltar plans to kill Sligon and then signal his compatriots to storm the castle, but by the time he reaches the castle, Valiant has escaped, and Boltar is unable to get close enough to Sligon to kill him. The Christian Vikings mistakenly believe that the burning torch Valiant thrusts at a pursuer is the attack signal, and soon an immense battle rages around the castle. Valiant succeeds in killing Sligon, and the Christians triumph over the traitors. Later, Valiant returns to Camelot, where he accuses Brack of being the Black Knight. Brack refuses to answer the charges and instead asks for a trial by combat, and although Gawain offers to fight in Valiant’s place, Valiant insists on fighting the more experienced Brack himself. After a prolonged sword battle, Valiant kills Brack, and then tells Gawain that he has brought Aleta back for him. Gawain laughingly explains that Ilene has told him the truth and that they have fallen in love. With a proud Aleta looking on, Valiant is then rewarded for his bravery by Arthur, who knights him with the sword Excalibur.