It is toward daybreak in Ezra's bedroom. Christine's ghostly form slips out stealthily from the bed. Mannon's dull and bitter voice remarks that Christine cannot bear lying close to her husband. Declaring that he wants to talk with her, Mannon lights the candle on the nightstand. Christine sits with her face turned three-quarters away from him in dread.
Mannon rebukes her for not wanting to remember that she ever loved him. Changing the subject, Christine asks if he heard Lavinia pacing like a sentry until two. When she asks about his heart, Mannon accuses her of wishing his death. Uneasy, he feels like he is waiting for something to happen. He knows the house is not his and that Christine is not his wife, that she awaits his death to be free.
Christine protests angrily that he just used her as his wife, however, as his property. Mannon retorts that, with the war, bodies have come to mean nothing to him. She had lied to him again with her declarations of love, letting him take her as if she were a "nigger slave." She has always made him appear the "lustful beast" in his own eyes.
Christine rebels and becomes deliberately taunting even as Mannon fearfully attempts to quiet her. She has never been his—she is Brant's mistress. Mannon rises in fury, calling her a whore and threatening her murder. Suddenly he falls back in intense pain and begs for his medicine. Christine retrieves a small box from her room and gives him his poison. Mannon realizes her treachery in horror, calls to Lavinia for help, and then falls into a coma.
Hearing noise from the hall, Christine hides the box behind her back. Lavinia enters and rushes to her father. With his dying effort, Ezra raises himself to a sitting position and points at his wife: "She's guilty—not medicine!" he gasps and then dies.
A stammering Christine confesses that she told Mannon of Brant but insists she did not do so to kill him. Her strength gone, Christine collapses in a faint. Lavinia discovers the small box. Horrified, she flings her arms around Ezra and beseeches him to stay with her, to tell her what to do.