"One of the apparent faults of King John is that it divides into two plays, Acts I-III and IV-V," in which the Bastard is first a "satiric improviser" and then later "seems lost and confused," or at least darker, and John in the later acts "falls apart, in a kind of hysteria" (Bloom 58).
"In the earlier scenes of the play Prince Arthur is a political pawn in the conflict between England and France; later, after he has been captured by the English, he becomes its touchstone of humanity" (Wells 111). Some Oxfordians think he represents the problematic case of eliminating Mary Stuart and reflects Oxford's discomfort with the matter (Ogburn and Ogburn 425; Anderson 216).
Hubert and executioners prepare to murder Arthur, who speculates wistfully, "So I were out of prison and kept sheep, / I should be as merry as the day is long" (IV.i.17-18). Hubert notes in an aside, "If I talk to him, with his innocent prate / He will awake my mercy, which lies dead" (IV.i.25-26) -- a realization occurring to other Shakespearean characters, in Merchant and Richard III, for example. Arthur notices Hubert's sadness. Hubert, fearing his own "womanish tears" (IV.i.36), shows the boy a document, and Arthur worriedly lisps, "Must you with hot irons burn out both mine eyes?" (IV.i.39). One suspects that one should not at this point be cheering on the executioners to put this little turd out of our misery, but....
Arthur whimpers about what a darling he's been to Hubert, but the man brings in the executioners. Arthur eventually gets to Hubert, and he sends them away, indicating that he'll do the deed himself. Ultimately, he chickens: he'll keep Arthur safe. Arthur is glad that Hubert has returned to his senses: "All this while / You were disguis'd" (IV.i.125-126). Hubert will merely report the death of Arthur.
John tries to convince himself and some lords that his recent second coronation should help quiet noise of revolt, but some think it has just drawn suspicion. Salisbury, in particular, takes up the "theme of superfluity" (Asimov 241): "To guard a title that was rich before, / To gild refined gold, to paint the lily, / To throw perfume on the violet, / ... / Is wasteful and ridiculous excess" (IV.ii.10-16). Pembroke thinks Arthur should be freed (although he knows of the command for execution), and John appears to agree to this. Hubert enters and speaks privately with John while Pembroke thinks the deed is already done. John announces that the boy is indeed dead, from a sickness. Salisbury practically accuses the King of murder, and he and Pembroke leave. John frets, realizing, unlike Macbeth, "There is no sure foundation set on blood; / No certain life achiev'd by others' death" (IV.ii.104-105).
A messenger brings word that the French are amassing their army. John doesn't understand how this could have escaped Elinor's notice until he hears that she is dead. "'What! mother dead?' John exclaims, rather bathetically, at the news" (Garber 274). Despite Shakespeare's playing fast and loose with dates and chronology in this play, he's gotten Eleanor's April 1st death correct, to the surprise of the critics. And Constance reportedly too, in a frenzy, died a few days earlier. John seems to be losing it.
The Bastard has been collecting funds but encountering unrest. He presents Peter of Pomfret, a prophet who predicts that John will give up the throne before noon on the next Ascension day (forty days after Easter). John has him imprisoned until execution at that very time, and then he sends the Bastard to exercise some diplomacy with the lords. During a brief lull in activity, it becomes clear that John is still trying to process the death of his mother (IV.ii.181).
Hubert returns and John demonstrates some very cheesy backpedalling regarding Arthur's supposed death (IV.ii.204ff). He pretends he did not intend to communicate such an order and that Hubert is to blame for a murder that has the kingdom in a tizzy. These dynamics closely resemble Elizabeth's wafflings concerning what ultimately was the order to have Mary Queen of Scots executed: note the phrase "my cousin's death" (IV.ii.248). Hubert then reports good news: Arthur is not dead (IV.ii.251). This is simultaneously an ironic blow and a good break for John, who naturally wants this news conveyed to the lords who earlier had blamed him. He sleazily excuses his own rage at Hubert a moment ago.
Historians are uncertain as to how Arthur met his end. Shakespeare in this scene has him trying to sneak out of prison. Arthur is extraneously disguised (IV.iii.4). He asks the ground to pity him so that he won't be too badly hurt in the fall and can continue his escape. He jumps and dies.
[As the audience's roaring applause dies down,] the lords arrive, planning to meet with Pandulph, and the Bastard summons them to the King. Just as he is about to announce that Arthur lives, they discover the corpse. The lords are outraged and the Bastard withholds blame. Hubert arrives with the news that Arthur is alive and Salisbury is furious. Hubert insists he left the boy alive. The Bastard has to prevent Salisbury and Hubert from dueling. When the lords leave, the Bastard questions Hubert, suspecting his involvement but sensing that there's more to this:
I am amaz'd, methinks, and lose my wayThe Bastard fears for England itself.
Among the thorns and dangers of this world.