The Duke of York enters the Parliament House in London with his two sons, Edward and Richard, followed by Norfolk, Montague, and Warwick. The lords wonder where the king has fled, and they discuss their successes in prior battles with the king's followers. Warwick points out that they stand before the throne, and he urges York to possess the royal seat. The lords ascend the diadem and York sits in the throne, resolved to seize the English crown once and for all.
Then, King Henry enters, with Clifford, Westmorland, Northumberland, Exeter, and other lords. Seeing York on the throne, Henry reminds his followers that York, who has killed the fathers of Clifford and Northumberland, wants to seize the throne. The lords want to attack York where he sits, but Henry reminds them that York's troops stand at the ready. He would rather fight with words and threats than to inflict bloody chaos on the Parliament House. Henry speaks to York, asking him to descend from the throne. The various lords insult each other, and Henry asks York what claim he has to the throne. York's father was merely another Duke of York, says Henry, but Henry's father was King Henry V.
Yet York reminds Henry that he lost the French lands that Henry V had conquered. Henry says the Lord Protector of the kingdom had lost it due to inattention. Richard and Edward urge York to seize the crown, but Henry's lords quiet them so Henry may speak. Though York thinks he has the lineage of a king, Henry assures him that he will not give up the position held by both his father and grandfather. But York declares that Henry's grandfather, Henry IV, got the crown unlawfully through rebellion. Henry knows his rights to the throne are based on a flimsy argument. He asks York if Richard II could have lawfully resigned the throne to Henry IV, but York insists rebellion caused the hand-over of power.
Hearing this, Exeter believes York and sides with him. Henry worries all his lords will abandon him. Clifford vows to fight on Henry's behalf, whether or not he is the true heir to the throne. Warwick announces that Henry must do right by York's claim, or he will send his soldiers into Parliament. Henry asks York to let him continue to reign while he lives, and he will then pass the crown to York and his heirs. York and Henry agree, but Clifford is appalled that Henry would think to disinherit his son and his right to the throne. Henry's lords are quickly disenchanted and depart to report to the queen. Henry sighs for his disinherited son, yet announces the terms of agreements for the eventual hand-over of the crown to York. York promises to honor Henry as king and not revolt against him, and the throne shall pass to the house of York. York agrees, descends from the throne, and embraces Henry. York and his men depart.
Henry and Exeter are joined by Margaret and Prince Edward. Margaret upbraids Henry, saying she wishes she had died before marrying him, rather than seeing him behave so unnaturally toward his son. Henry tries to excuse himself, saying that York and Warwick forced him into the agreement. Margaret asks him how he can be king and yet be forced to do anything. Appalled, she tells him he has undone his reign, and he now is allowed to reign solely thanks to the Yorks. He endangers himself by striking a deal with these wolves, who now encircle him like a trembling lamb, and he is wrong to think they will let him rule unharmed. If she had been there, she would never have let Henry make such a deal. Thus, she will distance herself from Henry until he undoes his agreement to disinherit their son. Margaret prepares to leave, while Henry asks his son if he will stay. Prince Edward says he will return only when they have had victory on the battlefield, and they leave.
Henry remarks on Margaret's behavior, saying that her love for her son has enraged her against York. He asks Exeter to help him be reconciled with his lords.
See 1 Henry VI and 2 Henry IV for extensive background about the struggle for the throne played out here. In short, York believes that he is the rightful heir to the throne because Richard II was forcibly removed from the throne by Henry IV, so all rulers thereafter have had an illegal claim to the throne. York's lineage stems from the eldest surviving brother of Richard II, who should have been the heir when Richard II died childless. Henry, on the other hand, is both the grandchild of the usurper and a relative of a younger brother of Richard II, making his claim to the throne entirely spurious, in York's eyes.
Henry makes his claim to the throne by evoking the name of his father Henry V, who was a very popular leader and who conquered much of France, to the appreciation of the English lords. While Henry's own ineffective ruling has led to the loss of those same territories, Henry nevertheless points to Henry V as proof of the validity of his reign. Henry IV may have been a usurper, but he became king, as his heirs did in turn, and that alone should be proof of his right to power.
Yet Henry is not cut out to be a powerful ruler, and he is not enthusiastic to defend his reign. Striking a deal with York to keep the throne during his lifetime but pass it to York thereafter, Henry effectively disowns his son by eliminating Prince Edward's right to become the next ruler. As Henry gets weaker, his French-born wife Margaret gets stronger and determines to set things right through the power of the armies, now at her command.
Margaret points out the essential problem with Henry's arrangement with York: by disowning his son, Henry has become an unnatural father and disrupted the normal pattern of familial relations and monarchal succession. His weakness has made the relationships of the royal family into a relative monstrosity, where a king gives up the crown but a queen leads the armies to recover it. Margaret is repeatedly accused of being unnatural, as a woman who takes up the sword and commands armies. That surely originates from Henry's denial of his own role as protector of his son, a task that Margaret must take up.
The severing of bonds between father and son recurs in this play in several spots. In one case, Henry watches two consecutive soldiers stripping the spoils of war from the bodies of men they have killed, discovering they have killed their own father and son, respectively. At York's own death, the camaraderie of his sons is destroyed and replaced with fraternal rivalry. When kinship ties are broken, all that remains is the will of the individual, which is most strikingly demonstrated in the awesome willpower of Richard, York's son, who eventually destroys everyone else in the way along his path to the throne.