Act four scene one starts with Gloucester speaking to an Old Man who seems to be talking on behalf of Edgar, still disguised as poor mad Tom. Edgar's lines are spoken in asides to the audience as it seems he is trying to avoid conversing with his father in case Gloucester recognizes his voice. The Old Man learns from Gloucester that he has recently become blind, but Gloucester admits that having eyes did not help him see the truth. Like Lear, being in this dependent state has given him sympathy for those who depend upon others. He asks the Old Man to find clothing for poor Tom, so the Old Man leaves. Gloucester asks his disguised son if he knows the way to the cliffs of Dover. Edgar says he does and agrees to take him there.

     In scene two Goneril is talking to Oswald about her husband, Albany. Oswald says that Albany has been acting strangely. He seems angry with Goneril. When Edmund enters, it becomes clear that Goneril is in love with him, so when Albany enters, it makes sense that he would be angry with his wife. A messenger reports that Cornwall has died. Goneril thinks that this will give Regan an opportunity to marry Edmund.

     Scene three finally goes back to Cordelia who is talking to the Gentleman who delivered Kent's ring to her. She realizes her father needs her help and vows to defend him. In scene four Regan sees Oswald who is bringing a letter from Goneril to Regan. Regan wants to open the letter as she suspects her sister is also interested in marrying Edmund, despite still having a husband, and Regan is jealous. She orders Oswald to kill Gloucester if he should find him, and they leave.

     In scene five Edgar claims to have taken Gloucester to the top of a cliff. He describes the scenery to the blind man, but it is clear he is lying. He then leaves Gloucester, who desires to kill himself, to jump off the edge. Gloucester falls to the ground right in front of him, and Edgar comes forward pretending to be a stranger at the bottom of the cliff who witnessed Gloucester's fall. Edgar says it's a miracle that Gloucester survived such a drop. He says he saw a demon at the top of the cliff who lead Gloucester to the edge. Once again, Gloucester seems to believe the lies. Lear then coincidentally appears and admits that he made a mistake in accepting his daughters' flattery. He knows they are trying to get rid of him, and they have fallen victim to their excessive desires. Despite Lear often ranting about nothing, Edgar remakrs that there is "reason in madness" because some of what Lear says is true. Lear states that he wants both Cornwall and Albany dead. He knows he has behaved like a fool, and he needs to be more brave and fight; then he runs off. After a gentleman happens by announcing the start of battle, Oswald finds Gloucester and wants to fulfill his promise of killing him. Edgar intercepts and kills Oswald instead. As a last request, the ever-obedient Oswald asks the disguised Edgar to deliver the letter to Edmund that Goneril asked him to bring. Edgar reads the letter and learns of Goneril's affection for Edmund. Edgar then takes Gloucester and leaves.

     In scene six King Lear has ended up with Cordelia where he has been sleeping to regain his strength and sanity. When he wakes up, he thinks he is dead; however, when he finally realizes he is with Cordelia, he has a moment of clarity. He asks her for forgiveness, for which she says there is no need. He ends with the admission that he is old and foolish.