King Henry VI, attended by nobles, is introduced to his new bride Queen Margaret by the Duke of Suffolk, who negotiated the marriage as part of a treaty with France. Suffolk hands the treaty to Henry’s uncle and Lord Protector, the Duke of Gloucester, who begins reading the treaty aloud. When Gloucester reads that Suffolk has committed Henry to surrendering the England-controlled French territories of Maine and Anjou, he drops the treaty in horror. After Henry, Margaret, and Suffolk leave for Margaret’s coronation, Gloucester passionately criticizes the treaty, warns the other nobles that England will lose all its French territory, and storms off.
Henry’s great-uncle Cardinal Beaufort and two other noblemen, Buckingham and the Duke of Somerset, discuss conspiring with Suffolk to topple Gloucester from power. After these conspirators leave, the Duke of Salisbury addresses his son (the Earl of Warwick) and the Duke of York, suggesting that for England’s sake they should protect loyal Gloucester from the ambitious conspirators. Warwick and York agree. Yet after Salisbury and Warwick leave, York, now alone, declares that he considers himself England’s rightful king and plans to usurp the throne, winning Salisbury and York to his side while letting the other nobles destroy Henry’s protector Gloucester.
Later, Gloucester’s wife Eleanor, the Duchess of Gloucester, hints to him that they should become king and queen, overthrowing Henry and Margaret. Gloucester rebukes the Duchess’s disloyalty. After Gloucester leaves, the Duchess meets a priest named Sir John Hume, who hints that the Duchess will become queen and says he has found conjurers to answer her questions about the future. Once the Duchess has left, however, Hume admits that Cardinal Beaufort and Suffolk are paying him to entrap her in treason as a way of ruining Gloucester’s position at court.
Later, York, Buckingham, and their guards burst in while the Duchess listens to conjurers question a spirit about the fates of Henry, Suffolk, and Somerset. York and Buckingham arrest the Duchess. Buckingham goes to alert Henry, while York meets with Salisbury and Warwick. At the meeting, York lays out his claim to the throne: he’s descended from King Edward III’s third son through his mother, whereas Henry is descended from King Edward III’s fourth son. Convinced York has a better claim to the throne, Salisbury and Warwick kneel to him.
At the Duchess’s trial, Henry exiles her to the Isle of Man and orders Gloucester to surrender the staff of the Lord Protector. Later, Henry summons Gloucester back. While he waits for Gloucester, various nobles tell him Gloucester is guilty of sordid crimes. When at last Gloucester appears, Suffolk orders him arrested for treason and held by Cardinal Beaufort’s guard until the trial. Henry allows Gloucester to be taken away, but he announces his belief in Gloucester’s innocence. Suffolk conspires with Margaret and Cardinal Beaufort to have Gloucester killed in custody. Otherwise, Henry will find some way to acquit Gloucester at the trial.
A messenger arrives and announces that Ireland is rebelling against English rule. After York is given the task of leading an army to put down the rebellion, he plans—while in Ireland—to incite an English rebellion against Henry, paying a former soldier named Jack Cade to pretend to be a long-lost descendant of royalty with a claim to the throne.
Suffolk pays two men to kill Gloucester. When Henry summons Gloucester to court for a trial, Suffolk volunteers to go get him—and quickly returns, announcing his death. A grief-stricken Henry laments Gloucester’s death. Shortly after, Salisbury and Warwick arrive trailing an angry crowd. Warwick explains that the common people have heard rumors that Gloucester was murdered, and Salisbury announces that they want Henry to exile Gloucester’s enemy Suffolk. If Henry won’t, the crowd plans to kill Suffolk themselves. Henry promptly exiles Suffolk.
Cardinal Beaufort comes down with a sudden illness and dies raving guiltily. Suffolk, sailing into exile, is killed by pirates whom York sent to murder him. Meanwhile, York’s cat’s-paw Cade starts a rebellion against King Henry, killing several noblemen while wreaking havoc around London. Yet when Buckingham and another nobleman named Old Clifford parley with Cade’s forces, Clifford convinces Cade’s rebels to turn on him. Cade flees and is soon killed.
After Clifford has announced the rebellion’s end to a jubilant Henry, a messenger announces that York has returned to England at the head of a fierce army, declaring his intention to “save” Henry from the secretly traitorous Somerset. Henry sends Buckingham to talk York down.
York plans to use his army to seize Henry’s throne, but when Buckingham comes and questions York, York claims he brought the army to England to save Henry from Somerset. Buckingham assures York that Henry has already imprisoned Somerset. Pretending relief, York tells his army to demobilize but orders them to meet him the next day, supposedly so that he can pay them what they’re owed.
After York goes and greets Henry, he spies Somerset—not in prison at all—approaching with Queen Margaret. Furious, York calls Henry a religious weakling and declares himself England’s rightful king. Soon the court has split into camps, supporters of York versus supporters of Henry. Battle breaks out. York kills Old Clifford, while York’s son kills Somerset. Henry and Margaret, realizing their side is losing, flee back to London to regroup. Meanwhile, York’s supporters—including his sons, Warwick, and Salisbury—celebrate their victory.