Back in England, Edward celebrates both his military victory and the fact that he has gotten his own way with regards to Spencer Junior. He asks Maltravers to read the list of executed rebels, and then gloats that Isabella's efforts to find French allies have failed thanks to the money he has spent there. Finally, he asks whether Spencer has issued a reward for Mortimer Junior's capture and dismisses the idea that Mortimer could have slipped out of the country.
As he has throughout the play, Edward here places too much stock in his authority as king. It is inconceivable to Edward that any harbormaster could have been "so careless of their King's command" as to allow Mortimer to escape, but this appears to be precisely what happened: whether through bribery or some other means, Mortimer managed to secure passage to France. Similarly, his certainty that Isabella no longer poses a threat now that he has paid off the French nobles smacks of arrogance, and speaks to his constant underestimation of those closest to him.
A messenger arrives from France with a letter for Spencer Junior from Levune. It explains both that Levune succeeded in buying off the French nobility and that Isabella, disappointed, went to Hainault with Kent and Mortimer Junior to raise an army. The news of Mortimer's escape and Kent's betrayal angers Edward, and he sarcastically “welcomes” both them and Isabella to England so he can meet them in battle. He is saddened by Prince Edward's involvement, however, even as he prepares to go with his followers to Bristol where he plans to confront the rebels.
The news of Prince Edward's involvement in the rebellion presumably hits Edward II particularly hard because of the familial relationship that connects them. Edward does not know that his son is involved in the rebellion only reluctantly, and instead assumes that the Prince actually supports the rebels' cause.