(Act Four is subtitled "John Brown's Body")
Joe visits Roy in his hospital room, afraid at first that Roy would not have forgiven him for refusing the job in Washington. Instead, Roy asks Joe to kneel before him and gives him a father's blessing, likening it to Jacob's in the Old Testament. Then Joe tells Roy he has left Harper and has been living with a man. Roy climbs out of his hospital bed, pulls the IV out of his arm and walks away, bleeding. When Joe goes to help him, Roy grabs him by the shirt and orders him to go back to his wife and never think of men again. Joe is confused, but Roy cuts him off and insists that he leave—he is furious, and he does not want Joe to witness the humiliation of Belize attending to him. After Joe leaves, Ethel comes to see Roy in his misery. Meanwhile, Prior reluctantly meets Louis on a bench in the park. Louis says he would like to make up—though not to move back in. Prior confronts him about Joe, attributing his knowledge to his "threshold of revelation." Then he tears into Louis for deserting him, telling him not to return until he has visible proof of the bruises he claims to feel inside.
Prior and Belize sneak down the corridor outside Joe's office in the Hall of Justice—they have come to spy on him. Prior walks boldly into the office and tells Joe that he looks just like the dummy in the diorama. When Joe asks what he is talking about, Prior mentions Harper, and then repeatedly insults him. Returning to Belize, Prior despairs at how attractive Joe is. A madcap scene ensues: Joe recognizes Belize as Roy's nurse and corners him and Prior, and Prior pretends to be a mental patient.
Belize meets Louis in front of the Bethesda Fountain, a huge statue of an angel in Central Park. Louis tells Belize he is worried for Prior, since he seemed delusional when they last met. In addition, Louis wants Prior to understand that he is no longer seeing Joe. Belize, unimpressed, tells Louis that Joe is an intimate of Roy Cohn's. Louis refuses to believe it, calling Roy "the polestar of human evil." He accuses Belize of making it up because he hates him. Belize angrily retorts that Louis has no idea what he is talking about, because he loves nothing but big ideas, like "America." By contrast, Belize says he knows America firsthand, and America is just like Roy, he says: "Terminal, crazy and mean."
Joe finally comes to see his mother Hannah at the Mormon Visitor's Center—she is angry that he has not returned her calls, at what she sees as his typical male insensitivity. He is looking for Harper, but she is nowhere to be found. Upset, Joe tells his mother he never should have called her, and leaves. Prior comes in, asking Hannah if Joe is her son—he says he wants to warn Joe about Louis's limitations. Then he starts to cry, and his health begins to collapse again. He asks Hannah to take him to the hospital.
Joe finds Harper on the harbor promenade in Brooklyn. She is barefoot and is wearing a thin dress in the driving rain—she threw her shoes in the river, she says, because Judgment Day is at hand. Joe tells her that he wants to come back to her.