Usurper Sligon (Primo Carnera), a worshipper of the old Norse god pantheon, along with other rebel Vikings, have forced the exile of the Christian royal family of the Viking kingdom of Scandia: King Aguar (Donald Crisp), his wife, and their son Prince Valiant (Robert Wagner). Aguar and his family come under the protection of King Arthur (Brian Aherne). When Valiant has grown to a man, he is sent to Camelot to undergo training as a knight under the tutelage of Aguar's family friend, the noble knight of the Round Table, Sir Gawain (Sterling Hayden).
During his wanderings, Valiant witnesses a clandestine meeting between a group of Sligon's Vikings and a black-clad knight. He is discovered, but with slyness and improvisation manages to elude his pursuers. During his flight, Valiant runs into Gawain, and after becoming convinced that Valiant is indeed the son of Aguar and hearing the prince's story of the mysterious Black Knight, who is not unknown to the knights of Camelot, Gawain takes Valiant to his king. Valiant is accepted by the king as a prospective knight, but first, like any other knight apparent, he has to undergo the rigors of squirehood. One of the royal knights, Sir Brack (James Mason), takes an extraordinary interest in Valiant and offers to train him, but Valiant is instead assigned to Gawain.
Some time later, Sir Brack offers to take Valiant to the place where the young prince has seen the Black Knight in order to backtrack the mysterious figure. Once there, they separate, but shortly afterwards Valiant is ambushed by a group of bowmen and barely escapes with his life and an arrow in his back. Wounded, he stumbles into the territory of King Luke (Barry Jones) and is taken in by his daughters, Aleta (Janet Leigh) and Ilene (Debra Paget). Upon recovery, Aleta and Valiant fall in love, but King Luke disapproves of Valiant's Viking origin and so their relationship must remain a secret for the time being. From Aleta, Valiant also learns that her younger sister Ilene is in love with Sir Gawain.
Valiant returns to Camelot and discovers, to his shock, that Gawain, who had grown worried over his squire, had tried to find him and had also run into an ambush by the Black Knight, likewise having escaped within an inch of his life. Noting that Sir Brack had temporarily disappeared around the same time, Valiant becomes suspicious, but on the advice of Gawain, suppresses his suspicion.
Some time later, Aleta and Ilene come to Camelot to attend a tournament held in their honor; as an added prize, the winner of this joust will win Aleta's hand. Valiant dons the armor of Gawain, who is too seriously wounded to participate, in order to win Aleta, but he fails and is unmasked. But then another contender appears and wins the bout before falling off his horse; this knight turns out to be Sir Gawain himself. Awakening on his sickbed, Gawain beholds Aleta and falls head over heels in love with her, and out of respect for his patron, Valiant does not dare tell him the truth.
For his act of presumption, Valiant is punished by being confined to his quarters and attending to his master. A mysterious messenger comes to the castle to see Sir Brack, and the same night King Aguar's seal is thrown through the window of Sir Gawain's chambers and lands at Valiant's feet. Realizing that his parents are in trouble, Valiant immediately leaves Camelot, leaving a bewildered Aleta behind. But as he prepares to return to his home, he is ambushed and captured by Sligon's Vikings and the Black Knight, who reveals himself as Sir Brack. Brack has made a pact with Sligon; for delivering King Aguar's family, Sligon will assist Brack in conquering Camelot by becoming the King over Britain.
Shortly, Aleta, who is unwilling to let Valiant run off, arrives at the scene and is captured herself, and the two are brought to Thule, where Sligon prepares to execute them and Valiant's captured parents. However, a group of Christian Vikings, led by Aguar and Valiant's old friend Boltar (Victor McLaglen), stage a revolution, and Boltar infiltrates the castle. Valiant manages to escape his cell and team up with Boltar, who intends to assassinate Sligon, and have Valiant give the attack signal to their cohorts once Sligon has fallen. But Valiant is discovered before Boltar manages to kill Sligon, and during his struggle with a guard a false signal is given, which makes the Christian Vikings attack prematurely. Just as things seem bleak, Valiant manages to set fire to several parts of the castle, throwing the defenders into confusion, after which he is able to slay Sligon in single combat.
Some time later, Valiant returns to Camelot with Aleta and accuses Sir Brack of treachery before the king and the assembled Round Table. Sir Brack calls for a trial by combat to the death, and despite Gawain's protests and his offer to fight in Valiant's stead, the young prince accepts the challenge. After a long and protracted fight, he succeeds in killing the traitor with his father's mystical broadsword, the Singing Sword. Valiant offers Aleta back to his master, but Gawain stays his hand; during the long period of worry over their loved ones, the older knight has finally come to learn the truth, and he and Ilene have fallen in love. In the end, having redeemed his honor by exposing the traitor, Valiant is made a fully privileged Knight of the Round Table.
New York Times review, April 7, 1954, by Bosley Crowther:
Have you read any good comic books lately? Do you know what's going on with Prince Valiant, his close friend, Sir Gawain, and the other knights of King Features' Table Round? If you do, then you have a good idea of what to expect from the big CinemaScope film that Twentieth Century-Fox has concocted from Harold R. Foster's Prince Valiant cartoon.
For Director Henry Hathaway and his associates have whipped up this clanging costume film in precisely the spirit and the aspect of the comic-book original. The hero is a glowing idealization, a straight high-school four-letter man, dressed up in a black wig and the garments of a free-wheeling Arthurian squire. The villain is a double-crossing rascal in the plumage of a Round Table knight. And the action is a wide-screen conglomeration of Douglas Fairbanks and horse-opera derring-do.
In a full blast of a Technicolor and stereophonic sound, this lively adventure romance went on at the Roxy last night.
Mind you, we noted at the outset that this is a film of the cartoon, which is strictly a popularization of legends, with no pretense at all to history. Prince Valiant, as cheerfully invented in this new juvenile literature, is a Christian Viking in exile, accepted at King Arthur's court as a squire and apprentice to Sir Gawain, who is an all-American with the spear and the sword.
From Sir Gawain, our apple-cheeked hero learns how to joust and duel. And from Aleta, the beauteous daughter of King Luke, he learns the tenderness of love. Armed with these powerful inspirations, he is able to challenge Sir Brack, the treacherous knight who would unthrone King Arthur. And challenge Sir Brack he does.
By far, the best part of the picture is a bigslam-bang rowdy-dow that occurs when two armies or Vikings put on a fight in and around a castle's walls. With Val (the nickname for Valiant) inside the enemy's stronghold, spreading fire and destruction, while his friends come battering in from outside, it all makes a fearsome conflagration of human passions and burning oil.
In this transcript of the funnies, Robert Wagner bounces boyishly as Val and James Mason slums graciously and grandly as the villainous Sir Brack. Janet Leigh wears tight dresses as Aleta, as does Debra Paget as her sister, Ilene, and Sterling Hayden scuffs his boots and acts embarrassed as the four-square old-timer, Sir Gawain. Behind an assortment of chin-whiskers and top-heavy Viking horns appear such grave or snorting worthies as Victor McLaglen, Brian Aherne, Donald Crisp, Basil Ruysdael, Primo Carnera and no telling who else, having fun.
As for the scenery and the jousting, it all looks very grand on the wide screen.
This ought to hold the kiddies, with their thirst for violence, through the Easter holidays.
Society as well as personalities of the entertainment world were represented last night at the premiere of Prince Valiant. The celebrities attending the screening included the Duke and Duchess of Windsor, Janet Leigh (who is featured in the film). Mr. and Mrs. William Randolph Hearst, Laurence S. Rockefeller, Phil Silvers, Sidney Kingsley, Mimi Benzell, Richard Tucker, Prince Christian of Hanover, Rita Gam, Sloan Simpson and Mr. and Mrs. Byron Foy.
The opening was recorded by the television cameras of Station WPIX. The Mutual Broadcasting System tape recorded interviews for re-broadcast today and the festivities also were recorded by the Voice of America and the Armed Forces Radio Service for broadcast overseas.