Kent aids Mortimer to escape the Tower and sail with him to France.
The queen's mission to France has failed and the prince urges her to return to England. Sir John of Hainault persuades them to go with him to Flanders, and when Kent and Mortimer meet up with them, they join up, planning to raise an army to attack the king.
Edward has executed the rebellious nobles, and he gloats that "The lords of France love England's gold so well / As Isabella gets no aid from thence." Spencer reads a letter from Levune telling about the efforts of Kent and Mortimer to raise an army in Flanders.
The queen and her followers arrive in England and prepare to attack Edward.
Spencer, Baldock and the king flee to Ireland from the queen's troops.
Kent turns against Mortimer and denounces "this unnatural revolt," observing that "Mortimer and Isabel do kiss while they conspire." When the others enter, he asks the queen what she plans to do with her husband. Mortimer, in an aside to the queen, says, "I do not like this relenting mood in Edmund." Spencer's father has been captured, and Mortimer orders him beheaded.
The king, Spencer, and Baldock, whose plans to sail for Ireland have been stymied by bad weather, have taken refuge with some monks, but Spencer has noticed "A gloomy fellow in a mead below" who he fears may have recognized them. Sure enough, a mower has informed on them and Rice ap Howell and the Earl of Leicester arrive with soldiers to arrest Spencer and Baldock for high treason and to take custody of the king. Edward is sent to Killingworth Castle.
At Killingworth, Leicester demands that the king surrender his crown. Edward protests, "But tell me, must I now resign my crown / To make usurping Mortimer a king?" The Bishop of Winchester tells him that the crown is for his son. Edward protests that his son is "a lamb encompassèd by wolves," but Leicester persists in demanding the crown. Edward takes it off, but puts it on again: "in this torment comfort find I none / But that I feel the crown upon my head, / And therefore let me wear it yet a while." They insist, and, as the stage direction puts it, "The KING rageth." Finally, he gives in. Leicester receives a message from the queen that Edward is to be handed over to Sir Thomas Berkeley.
Mortimer tells the queen that Spencer and Baldock have been executed. He proposes that the prince be made king with himself as protector, and the queen tells him to do whatever is necessary. A messenger arrives with a letter and the Bishop of Winchester with the crown, as well as the news that "we have heard that Edmund laid a plot / To set his brother free." Mortimer summons Gurney and Matrevis to take over from Berkeley the handling of Edward, so that only they will know where the king is. The queen frets that as long as Edward is alive, "What safety rests for us, or for my son?" Mortimer asks her, "shall he presently be dispatched and die?" and the queen replies, "I would he were, so it were not by my means." Mortimer orders Gurney and Matrevis to do whatever they can to make the king's life miserable." The queen pretends to be sympathetic to the king and gives Matrevis a ring to give the king "as witness of my love." When they leave, Mortimer tells her, "Finely dissembled," and suggests that she continue to pretend to love the king when her son enters.
The prince is accompanied by Kent, and Mortimer observes, "If he have such access unto the prince, / Our stratagems will soon be dashed." The queen urges him, "Use Edmund friendly, as if all were well." But Kent quickly sees through their pretense to be upset at Edward's abdication. Mortimer says to Kent that he should be the young new king's protector, but Kent says that his mother should have that role. And when the prince says he doesn't want to be king without talking to his father first, Kent says that he should do that. The queen retorts, "Brother, you know it is impossible."
PRINCE Why, is he dead?
QUEEN No, God forbid!
I would those words proceeded from your heart.
Mortimer points out that Kent was part of the plot that led to Edward's imprisonment, and Kent expresses his regret for it. When the prince takes Kent's side, Mortimer seizes him roughly. And when the queen takes Mortimer's side, Kent vows
Mortimer shall know that he hath wronged me.
Hence will I haste to Killingworth Castle,
And rescue agèd Edward from his foes,
To be revenged on Mortimer and thee.
Mathias and Gurney torment the king by giving him sewer water to wash in. They also shave his beard. Edward laments, "O Gaveston, it is for thee that I am wronged; / For me, both thou and both the Spencers died, / And for your sakes a thousand wrongs I'll take." Kent arrives, demanding to speak with the king, and is captured and taken to Mortimer. Kent complains, "O, miserable is that commonweal / Where lords keep courts and kings are locked in prison!"
Mortimer is resolved that the king must die because "The commons now begin to pity him." But he wants to make sure that he's not blamed for the king's death, so he has had a letter written in Latin that can be translated as either "Fear not to kill the king" or "Kill not the king," depending on where the comma is placed. By leaving it unpunctuated, he makes the letter ambiguous, so that "if it chance to be found, / Matrevis and the rest may bear the blame / And we be quit that caused it to be done." He also hires an assassin named Lightborne (as the note points out, a translation of "Lucifer"), whom he sends to Matrevis and Gurney with a secret message that Lightborne should be killed after he kills the king. Lightborne assures Mortimer that he's skilled in all forms of poisoning, including "take a quill / And blow a little powder in his ears," which is a variant of the way Claudius offed the elder Hamlet. When Lightborne leaves, Mortimer gloats, "I am Protector now. / Now all is sure. The queen and Mortimer / Shall rule the realm, the king, and none rule us."
The prince, the newly crowned Edward III, enters with a retinue that includes the queen and the Archbishop of Canterbury, who proclaims "Long live King Edward, by the grace of God, / King of England and Lord of Ireland!" Kent is brought in as a prisoner, and when Mortimer orders him beheaded, the young king tries to intervene but is overruled. Edward III asks, "What safety may I look for at his hands / If that my uncle shall be murdered thus?" The queen tells him, "He is a traitor. Think not on him. Come."
Matrevis and Gurney are surprised that Edward II has survived their treatment of him: He has been kept in "a vault up to the knees in water" supplied by the castle's latrines. Gurney says, "I opened but the door to throw him meat, / And I was almost stifled with the savour." Lightborne enters with the letter from Mortimer, and they interpret the Latin as saying that the king should be killed. They also read the note that says the murderer should be killed, too. So they give the keys to the dungeon to Lightborne, who orders, "get me a spit, and let it be red hot," as well as a table and a featherbed.
Lightborne recoils at the state of the dungeon, but pretends to be there with good news for the king, who sees through the ruse easily: "These looks of thine can harbour nought but death." The king's murder is vaguely described in the stage directions: "MATREVIS and GURNEY bring in a table and a red-hot spit." And by Lightborne's instructions: "So, lay the table down, and stamp on it, / But not too hard, lest that you bruise his body." Afterward, when Lightborne says, "Tell me, sirs, was it not bravely done?" Gurney stabs him and says to Matrevis, "Come, let us cast the body in the moat, / And bear the king's to Mortimer, our lord."
Mortimer meets Matrevis, who tells him the deed is done and Gurney has fled, "and will, I fear, / Betray us both; therefore let me fly." Mortimer says, "Fly to the savages." Mortimer boasts to himself, "I stand as Jove's huge tree, / And others are but shrubs compared to me." The queen enters to say that her son has heard the news of his father's death, but Mortimer is unconcerned: "What if he have? The king is yet a child." But Edward III enters with lords and attendants to denounce Mortimer as "Villain!" and to proclaim that Mortimer should be executed and his head placed on his feather's hearse. Mortimer denies being responsible for his death, but Edward shows him the letter sent to order the murder. "False Gurney hath betrayed me and himself," Mortimer says aside. The queen pleads for Mortimer, who tells her, "Madam, entreat not. I will rather die / Than sue for life unto a paltry boy." And Edward says, "This argues that you spilt my father's blood, / Else would you not entreat for Mortimer," although he admits to one of the lords, "I do not think her so unnatural." He sends her to the Tower to await further trial. The queen exits, and a lord enters with the head of Mortimer. Edward II's hearse is brought on as the young king says, "let these tears distilling from mine, / Be witness of my grief and innocency."