Edmund opens alone, and what he says before anyone enters tells you everything. He is not bitter and confused: he is clear-eyed and decided. He refuses the category of bastard, which he sees as a legal fiction designed to protect inheritance at the expense of merit. His dimensions are as well compact, his mind as generous, his shape as true as any legitimate son. The accident of his birth means nothing; the system that punishes him for it means everything. "Now, gods, stand up for bastards," he says. Then he gets to work.
The letter he produces, supposedly written by Edgar, is his own invention. Its contents are calibrated to infuriate a father: Edgar supposedly wants the old to yield to the young, and hints that if Gloucester were to sleep permanently, Edgar would share the revenue with Edmund. When Gloucester enters, Edmund makes a performance of hiding it. The psychology is precise: a letter tucked away is more interesting than one openly offered. Gloucester demands to see it. Edmund hands it over with theatrical reluctance.
Gloucester reads and explodes, calling Edgar a villain six times in as many lines. Edmund plays the loyal son who wants fairness: perhaps Edgar wrote this only as a test of Edmund's virtue, perhaps they should hear him out. He offers to arrange for Gloucester to overhear a conversation between the brothers. Gloucester, desperate to believe his son is not a monster, agrees.
Left alone briefly, Gloucester blames the disorder on eclipses; cosmic forces portending unnatural divisions between children and parents. Edmund, in soliloquy, dismantles this with contempt: "when we are sick in fortune... we make guilty of our disasters the sun, the moon, and the stars." He was who he is regardless of what star was overhead at his birth. Blaming heaven for what men choose to do is, he says, "the excellent foppery of the world."
Edgar arrives and Edmund manages him just as smoothly: warning him their father is furious, advising him to stay away and go armed. Edgar suspects nothing.
The scene ends with Edmund naming what he has found: "A credulous father, and a brother noble, whose nature is so far from doing harms that he suspects none; on whose foolish honesty my practices ride easy." He does not gloat. He simply observes, and moves on.
