A messenger from France arrives in the English court, demanding that King John abdicate his throne in favor of his nephew Arthur. The messenger speaks for King Philip of France, who supports Arthur’s claim as the rightful heir to the throne. When John refuses to step down, France threatens war.
The Bastard and his younger brother enter to dispute the inheritance of their late father’s land. John rules that the Bastard has the right to the lands, because a wife’s offspring becomes a father’s heir, no matter who the actual father is. John’s mother, Eleanor, takes a liking to the Bastard, because it is rumored that his father was her son and John’s brother, Richard the Lionhearted. She proposes that he leave his lands to his younger brother and join her armies under the name of the Bastard of Richard the Lionhearted. He agrees, and John knights him as Sir Richard Plantagenet.
In France, King Philip and his forces prepare to attack the English-held town of Angiers if its citizens don’t swear allegiance to Arthur. John and his armies arrive. Each king then asks Angiers’s citizens whom they support as the king of England, but the citizens are noncommittal, saying they support the rightful king. Philip and John’s armies go to war, but they are so equally matched that neither side wins. The citizens of Angiers still won’t decide between them. The Bastard then suggests that the English and French armies unite to conquer the disobedient town, then resume their fight with each other. They agree and prepare to attack. At this point, the citizens of Angiers suggest an alternative. They suggest that Philip’s son Louis should be married to John’s niece Blanche. Louis and John are pleased with the idea, because it strengthens John’s ties to the throne, and Louis gains English-held territory in France. The Bastard marvels at the fickle minds of the nobles. Meanwhile, Arthur’s mother, Constance, is upset that Philip proves so quick to abandon his support for her son.
Soon after Louis and Blanche are married, Pandolf, an ambassador from the pope, arrives. He charges John with having disobeyed the pope in a matter relating to an archbishop’s post, but John is not about to obey the orders of the distant pope. Pandolf excommunicates John and order Philip to withdraw his alliance and go to war with England. Philip hesitates, but the pressure soon leads him to yield, and he breaks with John.
After inconclusive battles in which the English capture Arthur, John prepares to return to England, leaving his mother in charge of English-held French territories and sending the Bastard ahead to ransack the coffers of the English monasteries. John instructs Hubert to look after Arthur and then asks him surreptitiously to kill him. Meanwhile, Pandolf tries to encourage the French to fight, suggesting to Louis that he now can lay the same claim to the English throne as Arthur, because he has married into a branch of the English royal family. Louis agrees to attack England.
Hubert prepares to kill Arthur, but he is so enchanted with the young prince’s innocence that he is unable to go through with it. He tells Arthur that no one can know he is alive. Meanwhile, John’s lords have asked for Arthur to be released, so John agrees to order Arthur’s freedom. Hubert enters and reports that Arthur is dead; the lords believe Arthur was assassinated and depart to join Louis’s army. The Bastard arrives, reporting that the people are not happy about John robbing the monasteries, and they predict John’s downfall. John yells at Hubert, accusing him of having tricked him into ordering the death of Arthur, which he claims he never wanted. Finally, Hubert reveals that Arthur is alive, and John, relieved, sends him after the departed lords to report the news.
Arthur tries to flee England but foolishly leaps off a castle wall and falls to his death. The lords come upon his body and are horrified at the brutality they believe was used to kill the boy. Hubert enters and reports that Arthur is alive; the lords point out Arthur’s body and accuse Hubert of having killed him. Hubert says Arthur was alive when he left him. The lords depart to meet Louis.
With so many of his lords having shifted their allegiance to the French, John decides to restore his relation to the Catholic Church. After Pandolf symbolically recrowns John in the name of the pope, John asks him to shut down the French army’s attack. When the Bastard hears of this new alliance with Rome, he is unhappy, but he convinces John to let him lead England’s army just in case the French don’t desist.
John’s departed lords swear allegiance to Louis. Pandolf arrives with news that John has reconciled with Rome and tries to dissuade Louis from attacking, but Louis says he won’t be ordered around by anyone. The Bastard arrives to speak to Louis and threatens him with destruction at the hands of the English army unless Louis retreats. Each side prepares for battle.
A French lord is wounded, and he tells the English lords that Louis planned to kill them if he won. He urges them to rejoin John, and they do so. Louis’s reinforcements are lost at sea, greatly dimming his prospects of victory. Meanwhile, the Bastard meets Hubert, who reports that John has been poisoned by a monk at a monastery, where he had been awaiting a report from the Bastard. The English lords and John’s son Prince Henry gather around the ill king. The Bastard reports that he has lost many of his men, who drowned in a tide.
John dies from the monk’s poison. The Bastard prepares to attack Louis, but the nobles report that Pandolf had just brought them a peace treaty from Louis. The Bastard and the lords swear allegiance to John’s son, Prince Henry, and the Bastard celebrates England’s new peace, speaking of how the kingdom will never be conquered as long as it remains united.