Salisbury, Pembroke, and Bigot meet on the field, astonished that King John's forces have proven to be so powerful. Count Melun, a French nobleman, enters; he is wounded, and he urges the English lords to turn back from the path of their rebellion and seek out John to plead for his mercy. Melun reports that if the French win that day, Louis has ordered the English lords to be beheaded. The English are astonished, but Melun insists that he is telling the truth; he will die soon and has no reason to deceive them. Salisbury believes Melun and thanks him. He urges his companions to return to John.
Louis enters, remarking on the strength of the English army. A messenger arrives to report the death of Melun, the departure of the English lords, and the sinking of his army of reinforcements. Louis is dismayed at the news; with his reinforcements annihilated, his chances of victory are now very slim indeed.
Hubert and the Bastard encounter each other in the darkness. Hubert reports that the king has been poisoned by a monk. He adds that the English lords have returned to John, bringing his son Prince Henry. The Bastard replies that he has lost his men, who were drowned in the rising tide on the flatlands that night. He asks Hubert to escort him to the king's side.
Prince Henry discusses his father's health with Salisbury and Bigot. Pembroke reports that John can still speak. Henry mourns the fact that his father's mind has been destroyed by the sickness, even while his body still seems in good health. John is brought in, babbling. He tells Henry that he has been poisoned. The Bastard arrives, and he reports that Louis approaches unimpeded because the Bastard's forces have drowned.
King John dies. Henry marvels at the transitive nature of the world, where what was once a king can become a meaningless pile of dust. The Bastard swears to avenge the king's death, and turning to the lords, orders them to assemble their forces to help repel the French from their land. Salisbury reports that Pandolf recently visited them with an offer of peace from the Dauphin. The Bastard wants to attack anyway, but Salisbury says the peace has been agreed upon.
They discuss John's burial, and the Bastard swears to serve Henry. The other lords follow suit. The Bastard speaks of the suffering they have endured and comments that England has never been in danger of being conquered, except when it was divided against itself. Now that the lords have returned to the allegiance of their English king, England is strong again. Nothing can weaken England if its citizens remain loyal, he says.
This play refers in passing to King John's plundering of the monasteries, an action that caused much disagreement during John's actual reign. When he is poisoned by a monk, we see John die as a result of his policy toward the monasteries, despite the play's inexplicable underemphasis of that important aspect of his reign. (His other memorable action, and one of the most important in medieval English history, was his agreement to sign the Magna Carta granting certain inalienable rights to his lords. This document became an important legal foundation for such later landmarks as the United States Constitution, and represents the single lasting deed from John's reign as king. It is not mentioned in Shakespeare's play.)
The Bastard's unswerving loyalty to John makes him spur on the returned English lords to attack Louis, but a peace treaty has been made off-stage between Pandolf and the intractable Louis. Echoing the events outside Angers when the French and English geared up to attack the town but canceled the assault at the last minute, the Bastard here winds up for battle only to have his plans put on hold. It makes for an anticlimactic ending: Battles dwindle because troops were drowned or lost at sea, and enemies seem to come to a peace treaty by default, and offstage at that. The ending suggests that the peace will not last, because the Bastard is still ready to fight--and we know Louis was anxious to try to gain the English throne.
The Bastard speaks the last lines of the play, focusing on the idea of the impenetrable English nation. Yet England is not totally unconquerable, for the Bastard hints that the only real threat to England's power has been when its citizens turn against it. That he speaks these lines after the lords swear allegiance to Henry makes his speech seem like a warning for Henry against these allegiance-shifting lords or an admonishment of the lords themselves. But it also serves as a look ahead at the coming centuries of internal disputes that tore the country apart in the Wars of the Roses--disputes that were not yet completely finalized in Shakespeare's own time.