As trumpets sound, Edward, Spencer Senior, Spencer Junior, Baldock, and Levune appear, and they have a number of nobles (Kent, Warwick, Lancaster, and Mortimer Junior) under guard. Edward is boasting about his victory, which he attributes to “justice” rather than the “chance of war.” Still mourning Gaveston's loss, he looks forward to executing the nobles.
Edward's insistence that he is responsible (morally or tactically) for his victory is a mark of arrogance in a play where "fortune" figures prominently. As more and more characters rise to power and then fall, it becomes increasingly clear that they are at the mercy of forces beyond their control—including, as Edward says here, simple "chance."
Kent argues that the nobles killed Gaveston for the good of both the country and Edward himself, and Edward sends him away. He then disputes the idea that the nobles acted in “regard” of him by ignoring his request to see Gaveston once more, and killing him in an ambush. Warwick and Lancaster, however, dismiss Edward's threats, saying they would rather die than “live in infamy under such a king.” In response, Edward sends them off for execution under the guard of Spencer Senior.
Kent's definition of loyalty continues to clash with Edward's in this scene. As Kent describes it, the nobles' rebellion was actually a roundabout demonstration of their allegiance to both England and its monarch, since Gaveston was usurping Edward's place as king (Kent describes Gaveston as being removed from Edward's "throne"). Edward clearly disagrees and continues to complain of the nobles' disregard for his wishes. This in turn cements Lancaster and Warwick's opinion of Edward as unworthy of the throne. As they see it, it would be dishonorable not to rebel against Edward, even at the cost of their own lives.
Mortimer Junior laments the state of the country, which he addresses directly: “England, unkind to thy nobility, / Groan for this grief, behold how thou art maimed.” Edward gives orders for Mortimer's imprisonment, and the latter is taken away under guard, complaining that he deserves a higher “fortune” than this. Edward himself than leaves, celebrating the victory that has symbolically “crowned him King anew.”
Mortimer's words combine what appears to be genuine patriotism with personal ambition. On the one hand, his concern for the welfare of the country seems authentic. His complaints at being imprisoned, however, hint at the extent of his personal pride. In fact, he describes himself as "aspiring" even to "heaven." Mortimer ultimately pays for this hubris, not so much in the sense that he is punished for it, but in the sense that "fortune" proves indifferent to his plans for himself.
Spencer Junior instructs Levune to go to France and bribe the king and nobility there to withhold their support from Isabella: he suspects that she and the English nobility have been plotting to make Prince Edward king. Levune agrees, and Spencer urges him to leave as soon as possible
Tellingly, it is Spencer Junior rather than Edward himself who finally realizes the danger that Isabella poses and takes steps to undermine it. His attempts to counteract Isabella's pleas do in fact prove largely successful, but are not enough to prevent her from returning to England with an army.