A few moments before the end of the previous act, Orin appears before his father's body in the study. Ezra's face in death is another startling reproduction of the face in the portrait, resembling the "carven face of a statue." Orin's face in the candlelight resembles these in turn. As Orin addresses his father, Lavinia appears silently in the doorway.
"Death becomes the Mannons," exclaims Orin. For him, Ezra was always the "statue of an eminent dead man," cutting the living dead for the impropriety of their living. Lavinia locks the door and rebukes her brother: to think that Ezra boasted so highly of Orin's bravery. Orin grins bitterly. At the front, he would only volunteer for extra danger in fear of anyone discovering that he was afraid. He recalls killing a Reb face-to-face in the fog one night and then another just like him. The war meant murdering the same man again and again until he had killed himself. In his dreams, the faces of his victims change, becoming his, Ezra's, and others.
Orin continues and says that he got his wound at Peterburg when he walked out to enemy lines with his hand extended, deciding it would be a great joke on the generals if the soldiers suddenly reconciled. Once wounded, he went mad. His comrades joined him, and they captured a new part of the Rebel line. Lavinia urges him to forget and assures him she thinks him brave.
Frustrated, Orin changes the subject and tells Lavinia that Christine has already warned him of her madness. Lavinia implores him to listen, presenting Christine's pillbox and calling upon her father to make Orin believe. Orin dismisses her delusions saying that she has always been her father's daughter. He takes the box and puts it into his pocket.
Calculatingly Lavinia teases that Orin certainly would not let their mother's paramour escape. Orin flies into a rage, forcing his sister to his knees and commanding her to retract her lies. Lavinia calmly insists that she tells the truth, proposing that they watch Christine until she goes to meet Brant herself. Orin agrees to her plan.
Suddenly Christine knocks at the door fearfully. Lavinia commands Orin to feign that he has done as his mother wishes. As a test, she snatches back the pillbox and places it over Ezra's heart. Orin opens the door to a desperate Christine, who shrieks upon seeing the box. Orin laughs with savage irony, recalling how he believed he had returned to his island of peace. Christine is his "lost island." He stumbles out.
In Mourning Becomes Electra you write: "Oedipus was the Theban king who unwittingly killed his father and MURDERED his mother." [Emphasis mine].
It should read: "Oedipus...MARRIED his mother!"
(Oedipus' mother Jocasta did commit suicide after learning her lover was her son. Oedipus however did NOT "murder" her.)