The theme of incest is prominent in Mourning Becomes Electra as a deliberate motivator for, or an undercurrent beneath, many of the characters’ actions. Both members of the parental generation, Ezra and Christine Mannon, have behaved in immoral or sinful ways. Each of their children, Lavinia and Orin, is strongly devoted to the opposite-gender parent, and these attitudes strongly affect their subsequent actions, including murder and suicide. The extreme closeness within the family is portrayed as not just claustrophobic but unnatural. The character of Adam Brant serves as the linchpin connecting the parents and children to the idea of retribution.
In the complex plot of Eugene O’Neill’s trilogy, Adam believes that Ezra, who is a cousin on his father’s side, killed Adam’s mother. While Ezra is away serving in the Civil War, Adam has an affair with Christine, Ezra’s wife. Discovering her mother’s adultery prompts Lavinia to avenge her father’s death. Her deep love for her father and hatred of her mother exemplifies the psychological idea of the Electra complex. O’Neill does not indicate that this love was consummated, however.
Orin is similarly connected to his mother, manifesting the Oedipus complex. These feelings propel him to join his sister’s plot, but it is Adam, his mother’s lover, who is his target. He later joins his mother in dying by suicide as she had done. The parents’ misdeeds are also transmitted to the children as desire for each other, as Orin tries to convince his sister to have sex with him.