O'Neill's drama is built on Aeschylos' "Oresteia". The Greek drama is about murder and retribution in Agamemnon's family. As the leader of the victorious Greek army returns from the Trojan War, his unfaithful wife, Clytemnestra, makes her lover, Aegisthos, slay her husband. The children, Electra and Orestes, take it on themselves to revenge this murder: Orestes kills his mother and the usurper. Finally, since Orestes is haunted by the ghosts of his guilty conscience, the moral and legal case has to be decided, which crime is worse, Clytemnestra's or Orestes' - and the gods decide in Orestes' favour.
O'Neill did not only use the "Oresteia" as his blueprint, but also the psychoanalytical theory of Dr Freud, who borrowed some of his central terms from Greek mythology. O'Neill deviated from Aeschylos (see below), where he followed Freud closely:
The drama plays in 1865/66. General Ezra Mannon (Agamemnon) has returned from the Civil War, his wife Christine (Clytemnestra) hates him because to her he is a hardened, unfeeling male chauvinist and her daughter Lavinia (Electra) blindly hates her mother as she loves her father. Ezra is prepared to be a better man now but his wife can't forgive him. Knowing that he has a weak heart she brutally tells him that she has a lover, and when his expected heart attack comes on, she gives him poison. As soon as Orin (Orestes) has eliminated his mother's lover and Christine has committed suicide, Lavinia transforms herself into her mother in her looks and behaviour because, of course, she envied her and wanted to take over her role. Orin is an especially pitiful case. Whereas in the Greek drama he is able to act strongly and find redemption, here he is a neurotic weakling and perishes, for, of course, since Lavinia changes perceptibly into her mother, he begins to lust for her (having had no success with his mother as long as she was alive), and as Lavinia doesn't comply with his wishes, Orin can't bear it any longer and kills himself. Lavinia feels that life or sexual fulfilment are not for her, and so she locks herself up in their house for the rest of her life: the dead prove to be stronger than the living.
On the whole O'Neill 's trilogy is full of blood, horror, gloom and depression, but it is no longer a tragedy. The Greek drama played a public role in classical Athens - politically, religiously, morally - and since the gruesome events took place on the state level, were carried out by public representatives and supported or hindered by the gods, they carried weight and universal meaning. O'Neill restricts the gruesome events to the personal sphere, where they appear mainly as macabre. Tragedy is turned into melodrama which doesn't shatter you any more nor does it concern you very much, as the "Oresteia" concerned the spectators in Athens and might still concern spectators today. By adhering to Freud's ideas O'Neill sacrifices poetic truth, feelings are too often expressed too directly and explicitly, as if taken from the psychological handbook. More often than not one cannot help feeling that his drama could easily be turned into a comic strip or a parody, it is simply too unlikely. I guess this depressing parable about sexual frustration is not so symptomatic of the time (1931), when it was written, as it is of O'Neill's troubled mind.