At Berkeley, Gourney and Maltravers marvel at the fact that Edward has not yet died, despite being kept in a wet and dirty cell. They therefore decide to “assail his mind another while,” since he seems physically capable of withstanding his circumstances.
Significantly, Edward's deterioration while in prison is entirely internal. As Gourney and Maltravers note, Edward remains outwardly healthy. Edward's state thus parallels England's descent into civil war and political turmoil, particularly because Mortimer Junior has a hand in both: acting on orders from the Protector, Gourney and Maltravers decide to hasten Edward's decline into madness.
Just then, Lightborne enters and hands Mortimer Junior's letter to Gourney and Maltravers. Lightborne also shows them the token Mortimer gave him, and—in asides—Gourney and Maltravers discuss the fact that Lightborne is there to murder Edward and then be killed himself. Maltravers accordingly gives Lightborne the keys to Edward's cell, and Lightborne asks Maltravers and Gourney to fetch a table, a feather bed, and a hot spit.
Gourney and Maltravers's willingness to betray Lightborne foreshadows Gourney's later willingness to betray Mortimer. The fact that Mortimer does not recognize that this is a possibility, even after labeling Kent dangerous on similar grounds (i.e. his betrayal of Edward II) suggests that power has made Mortimer overconfident, and also perhaps that Mortimer’s rather blunt personality and limited ability with language makes him insensitive to the subtleties of life.
Now alone, Lightborne finds Edward, who suspects that Lightborne is there to kill him. Lighborne denies this, saying Isabella has sent him to enquire after Edward's well-being. In response, Edward describes the conditions in which he is held prisoner: his cell is in a cess-pool, he is given little to eat, and his jailers continuously make noise to prevent him from sleeping. As a result, he says, his “mind's distempered and [his] body's numb.”
Edward's words in this exchange reveal the full extent of his deterioration. Lack of sleep and food have made his mind "distempered," as evidenced by his confused behavior toward Lighborne: Edward is alternately suspicious of Lightborne and desperate to tell his story to him. Edward's sense of his physical self is also disturbed, perhaps in part because of the conditions in which he is being kept. He remarks, for instance, that he does not know whether he has limbs or not. Like Edward's mental state as a whole, this comment is symbolically significant, as it parallels the fragmented state of England itself.
Lightborne, claiming to be moved, urges Edward to lie down on the feather bed. Edward is still suspicious, even when Lightborne once more protests his innocence. In his uncertainty, however, he gives Lightborne a jewel to try to win his favor. Edward also tells Lightborne to “know that [he is] a king,” but is then immediately overcome by grief at the loss of his crown. Lightborne simply urges Edward to sleep again. Edwards does sleep , though fitfully: as soon as he has begun to drift off, he starts awake, saying that something tells him he will die if he falls asleep. He once more question why Lightborne has come, and Lightborne now admits the truth, calling Maltravers and Gourney into the room.
Edward's gift of the jewel, coupled with his reminder that he is a king, echoes much of the action from the first half of the play, when Edward lavished presents on Gaveston and insisted on his right to absolute rule. Given Edward's current circumstances, however, the parallel is bitter and ironic: the fact that Edward here gives the present to his killer underscores the role that his earlier behavior played in his downfall.
Maltravers and Gourney hold Edward down while Lightborne kills him with the spit. Fearing that Edward's screams will have been heard, Gourney quickly stabs Lighborne. The two men then leave, intending to take Edward's body to Mortimer Junior after throwing Lightborne's in the moat.
Although it is not clear from the stage directions, Marlowe's depiction of Edward's murder is based on a widely circulated rumor that he was rectally impaled with a heated spit. Although this is probably not what happened to the historical Edward (in fact, it is unclear that Edward was murdered at all), the story clearly arose because of Edward's suspected homosexuality: the murder method is a gruesome parody of anal sex, and therefore a kind of "justice" in the eyes of a homophobic society.