The "Black Prince" of England remains in France to guard the lands taken by his predecessor-father.

In 1359, after decades of war, King Edward III of England has regained control of disputed territory in northern France. With the French king being held prisoner in London, the French nobles are asked to sign a truce laying down their arms and recognizing King Edward as the rightful ruler of Aquitaine. Although they are guaranteed ownership of their estates, some of the nobles, including Comte Robert De Ville, are angry about their defeat and express hostility toward the king. Edward III warns the nobles that any act of aggression will be treated as treason, then, after they leave, greets his son, Prince Edward. The prince, a fierce fighter, is surprised by his father's decision to return to London and make him Duke of Aquitaine. Promising to send reinforcements, Edward III departs with most of the English Army, leaving the prince with only a small contingent of men. Meanwhile, De Ville, intent on overthrowing the English, persuades his friends to ally with Du Gueselin, the powerful regent whom they want to have proclaimed Lord High Constable. While De Ville and his cohorts are secretly rebuilding their troops, Edward is approached by a group of French peasants, led by Gurd, who tell him that the nobles are overtaxing the peasants and forcing them to participate in illegal weapons training. After Edward issues a proclamation banning both practices, he is surprised by a visit from Lady Joan Holland, the widow of a large Aquitaine landholder. Joan, the elder sister of John, the young Earl of Kent, flirts with Edward, her childhood sweetheart, but insists on residing in her late husband's estate, even though Edward protests that he does not have sufficient men to protect her. At De Ville's castle, the nobles learn of Edward's proclamation, and Libeau and D'Estell, De Ville's main allies, bitterly complain about Edward's "wooing" of the peasants. Seeing an opportunity to rid himself of Edward, De Ville sends a group of assassins, disguised as peasants, to Edward's castle, where they ask for an audience. Edward and his men best the assassins when they attack, and the leader, François Le Clerc, confesses that De Ville sent them. After learning that his plan has been foiled, De Ville decides to draw Edward out of his stronghold by kidnapping Joan, John, their younger brother Thomas and Genevieve, the children's nurse. When Edward hears about the kidnapping, he sets out with his men, and during the ensuing battle, is separated from his army. Edward and his devoted friend, Sir John, find themselves alone and behind enemy lines, and decide that the best way to find Joan is to infiltrate De Ville's castle. Pretending to be weary travelers, Edward and John stop at a nearby inn, where they make the acquaintance of a wily servant named Marie. With Marie's help, Edward steals the suit of black armor hanging over the inn's fireplace, then goes with John to De Ville's castle. Upon encountering De Ville, Edward, who has never before met the count face-to-face, states that he has vowed not to reveal his identity until the enemies of France have been defeated. De Ville challenges Edward, who calls himself the Black Knight, to defeat Libeau in a jousting competition, which Edward easily accomplishes. Admiring Edward's skill and forceful personality, De Ville hires him as a mercenary, and invites him and John, who is pretending to be Edward's squire, into the castle. When Edward is introduced by De Ville to Joan, she quickly deduces Edward's purpose and pretends not to know him. Edward and John attempt to rescue Joan and the others that night but when their plans go awry, Edward covers up by pretending to capture the fleeing Joan. Meanwhile, at the English stronghold, elderly knight Sir Bruce meets with the other knights and Gurd, who have been fruitlessly searching for Edward. Unable to risk engaging the French until reinforcements arrive, Bruce is forced to order his impatient men to wait. The next day, De Ville and his army ride out and meet with Du Gueselin, who has been declared Lord High Constable and amassed a large army. Knowing that Du Gueselin will recognize him, Edward attempts to avoid him, but the drunken Libeau, jealous that De Ville favors the mercenary, challenges Edward to a sword fight. While they are battling, Libeau accidentally raises Edward's lowered visor, and a shocked Du Gueselin recognizes him. Edward and John flee on horseback to De Ville's castle, where they convince the guards to release Joan and the others into their custody. As they ride toward the English castle, they are seen by some of the French Army and are chased. Edward rides in another direction to mislead their pursuers, and John safely delivers Joan to the English castle. There, John informs his friends of Edward's danger, but as they are about to leave, Edward arrives, and the English begin preparations to withstand a siege by De Ville and Du Gueselin. Joan and Edward steal a brief moment alone, and Edward promises her that they will spend the rest of their lives together. They are interrupted by the sound of alarms, and soon the French begin their assault on the castle. Still wearing his black armor, Edward leads his men in a ferocious defense. After a long battle, Edward is engaging in a sword fight with De Ville when Du Gueselin and the remaining Frenchmen are captured. After defeating his foe, who falls from the battlements to his death, Edward is embraced by a relieved Joan.