Battle is once more underway, and Edward's forces are in disarray. Spencer Junior urges the King to flee to Ireland, but Edward refuses, vowing to fight to the death in England, because he "was not born to fly and run away." Baldock responds by seconding Spencer's warning, saying that Edward's “princely resolution / Fits not the time.”
Edward's refusal to flee is based on a sense that retreat would be shameful for someone of his status. As they have throughout the play, however, Spencer Junior and Baldock ignore the nobility's (or king's, in this case) claims that they possess a special kind of honor by virtue of their rank. Instead, they pragmatically suggest that "princely" behavior is something to cast aside when it ceases to be useful. This once again undercuts the idea that nobility, and the actions associated with it, are innate qualities.
Kent appears in search of Edward, whom he now regrets turning against. Condemning the rebellion against his king and brother, he asks God to “punish this unnatural revolt.” However, he then chastises himself for speaking so openly, knowing Mortimer Junior will kill him if he discovers his loyalties have changed. Finally, Kent confirms for the first time in the play that Isabella and Mortimer are having an affair.
Kent's belief that the rebellion is unnatural stems both from Edward's position as king and from Kent's personal relationship to him. Just as revolting against a lawful king plunges a supposedly natural social hierarchy into chaos, so does betraying one's brother: since the hierarchy itself is based on blood relations, it is vital that members of the same family defend one another's rights.
Isabella, Mortimer Junior, Prince Edward, and Sir John now appear as well. Isabella appoints Prince Edward viceroy and rejoices in their victory, which she attributes to the justice of their cause. She concludes by telling her companions to deal with Edward II as they see fit, now that his “infortunate” destiny has resulted in his overthrow.
Interestingly, while Isabella describes Edward's fall from power as the result of bad luck, she does not apply the same concept of fortune to her own victory. Instead, she suggests that it is the result of moral worthiness and divine intervention. This corresponds to a broader pattern in the play, whereby characters refuse to believe that their own fates may be as arbitrary and undeserved as anyone else's.
Kent asks Isabella what she intends to do with Edward II, and Mortimer Junior grows irritated, saying that that is a matter for Parliament to decide. Privately, however, he warns Isabella that Kent may be having second thoughts.
Outwardly, Mortimer still seems concerned with the lawfulness of the rebellion: he refers Edward's fate to Parliament and insists that neither he nor Isabella has any authority in the matter (as they shouldn't, since neither has been appointed Protector at this point in the play). His aside, however, makes it clear that Mortimer is now concerned first and foremost with shoring up his own power, since he is alert to any hint of disloyalty.
As the group discusses the whereabouts of Spencer Junior and Baldock, Rhys ap Howell (a Welsh lord), and the Mayor of Bristol enter. Rhys ap Howell presents Spencer Senior, who has been taken prisoner, to Isabella and Prince Edward. He also explains that Spencer Junior and Baldock have fled with Edward II to Ireland—news which distresses Prince Edward and Kent. Isabella also professes to be upset about her "lord's ill fortune," but says she had no choice but to go to war. Mortimer Junior, however, brushes Isabella's qualms aside, saying that Edward “wronged [the] country and himself.”
In his attempts to "console" Isabella, Mortimer again pays lip service to the rule of law and the country's welfare. Because Edward's behavior jeopardized both England and the very authority of the monarchy itself, Mortimer says, he was obliged to try to "right" the situation. It is clear from his words elsewhere in the scene, however, that Mortimer is now mostly acting out of personal ambition rather than any sense of patriotism.
Mortimer Junior gives orders for Spencer Senior's execution, but the latter condemns Mortimer and Isabella as “rebels” before being taken away. Mortimer then orders Rhys ap Howell to deal with the remaining rebels in Bristol, while he and Isabella figure out what to do about Spencer Junior and Baldock.
Spencer Senior once more offers a definition of treason that casts anyone who "fights against his prince" as a rebel. He does not have much time to make his case, however, because Mortimer dismisses his words as "prating" (rambling or ranting) and sends him away: clearly, Mortimer will favor action over language as a ruler.