Edgar, disguised as Poor Tom, lurks outside in the cold. He comforts himself with the knowledge that, since he's hit rock bottom, at least things can't get any worse.
Then, of course, Edgar sees his father stumble out of the castle bleeding from his eye sockets.
Gloucester speaks bitterly. An old man who has been a tenant on Gloucester's property has been trying to help him, though Gloucester declares he doesn't need help for his blindness – he was actually more blind (couldn't see the truth about his children) when his eyeballs were intact.
Edgar listens in agony as Gloucester laments the loss of his good son, Edgar. Gloucester declares if he could only touch his boy again, it would be as good as having eyes.
The old man, who has been helping Gloucester, introduces father and son, who is still disguised as "Poor Tom," the beggar from Bedlam. (Why doesn't Edgar speak up and say "Hey! I'm your estranged yet loyal son, Edgar!")
Brain Snack: Shakespeare borrowed the Gloucester/Edgar/Edmund plot from Phillip Sidney's The Countess of Pembroke's Arcadia. In Book 2, Chapter 10 of the 1590 edition, the story's heroes encounter a blind king who is accompanied by his loyal son. It turns out that the loyal son has recently forgiven the king despite the fact that his father plotted to have him killed after the king's other kid (a treacherous and illegitimate son) stole his father's kingdom and poked out the old man's eyeballs.
Now, back to Lear. Gloucester recalls seeing this fellow ("Poor Tom") in last night's storm and briefly thinking of his son, whom he still hated at the time. Gloucester admits he's since learned he was wrong about Edgar, and sadly declares, "As flies to wanton boys are we to the gods / They kill us for their sport." In other words, Gloucester blames the gods for what's happened to him, not himself. And, in Gloucester's version, the "gods" are jerks.
Gloucester bids the old man to leave him into Poor Tom's care, and also to bring Poor Tom some clothes, because even madmen shouldn't be naked.
Though even the old man thinks this is a bad idea, as Poor Tom is also mad, Gloucester reveals a sense of humor by remarking, "'Tis the time's plague when madmen lead the blind."
Left alone with his father, Edgar still does not reveal his identity. For some reason, he keeps up his Poor Tom charade, talking nonsense to his father.
Gloucester asks Poor Tom to lead him to the edge of a cliff in Dover so Gloucester can jump off and end his misery (never a good idea).
Also, in case anyone wasn't clear that Gloucester plans to kill himself by jumping off a cliff, Gloucester makes explicit that Poor Tom won't have to lead him back. This is a one-way ticket.
Edgar agrees to take his father to his death. Or at least to Dover.