The main action of the play is the agon between Clytemnestra and Agamemnon. She attempts to persuade Agamemnon to step on a purple (sometimes red) tapestry or carpet to walk into their home. The problem is that this would indicate hubris on Agamemnon's part, and he does not wish to do this. Eventually, for reasons that are still heavily debated, Clytemnestra does convince Agamemnon to cross the purple tapestry to enter the oikos, where she kills him in the bath: she ensnares him in a robe and as he struggles to free himself she hacks him with three strokes of a pelekus. Agamemnon is murdered in much the same way an animal is killed for sacrifice with three blows, the last strike accompanied by a prayer to a god.
Whilst Clytemnestra and Agamemnon are offstage, Cassandra starts discussing with the chorus whether or not she ought to enter the palace, knowing that she too will be murdered. Cassandra has been cursed by Apollo for rejecting his advances. She has the gift of clairvoyance, but the curse means that no one who hears her prophesies believes them. In Cassandra's speech, she runs through many gruesome images of the history of the House of Atreus as if she had been a witness of them, and eventually chooses to enter the house knowing that she cannot do anything to avoid her fate. The chorus, in this play a group of the elders of Argos, hear the death screams of Agamemnon, and frantically debate on a course of action.
A platform is soon rolled out displaying the gruesome dead bodies of Agamemnon and Cassandra, along with Clytemnestra, who attempts to explain her action. Later, Aegisthus struts out and delivers an arrogant speech to the chorus, who nearly enter into a brawl with Aegisthus and his henchmen. However, Clytemnestra halts the dispute, saying that "There is pain enough already. Let us not be bloody now." The play closes with the chorus reminding the usurpers that Orestes, the son of Agamemnon, will surely return to exact vengeance.
In the palace of Argos, Clytemnestra, who now shares her bed and the throne with her lover Aegisthus, is roused from slumber by a nightmare: she dreamt that she gave birth to a snake, and the snake now feeds from her breast and draws blood along with milk. Alarmed by this, a possible sign of the gods' wrath, she orders her daughter, the princess Electra, whom in the meantime Clytemnestra has reduced to the virtual status of a slave-girl, to pour libations on Agamemnon's grave. A group of women (the libation bearers of the title) are to assist her.
Electra arrives at the grave of her father and comes upon a man by the tombstone, who has just placed a lock of his hair on the stone. As they start to speak, it gradually and rather agonizingly becomes apparent that the man is her brother Orestes (who had been sent away to the royal court of Phocis since infancy for safety reasons), and who has, in her thoughts, been her only hope of revenge. Orestes believes that he is the snake in his mother's dream, so together with Electra they plan to avenge their father by killing their mother Clytemnestra and her new husband, Aegisthus.
Orestes wavers about killing his own mother, but is guided by Apollo and his close friend Pylades, the son of the king of Phocis, that it is the correct course of action. Orestes and Pylades pretend to be ordinary travelers from Phocis, and ask for hospitality at the palace. They even tell the Queen that Orestes is dead. Delighted by the news, Clytemnestra sends a servant to summon Aegisthus. Orestes kills the usurper first, and then his mother. As soon as he exits the palace, the Erinyes, being only visible to him, begin to haunt and torture him as he flees in agony. The Erinyes do not hunt down Clytemnestra for killing her husband, but they do hunt down Orestes for his crime of matricide as is their function: to them, crimes against blood bonds are far more significant than crimes against marriage bonds.
The Eumenides (Ευμενίδες, Eumenides; also known as The Furies) is the final play of the Oresteia, in which Orestes, Apollo, and the Erinyes go before Athena and a jury consisting of the Athenians at the Areopagus (Rock of Ares, a flat rocky hill by the Athenian agora where the homicide court of Athens held its sessions), to decide whether Orestes' murder of his mother, Clytemnestra, makes him worthy of the torment they have inflicted upon him.
Orestes is tormented by the Erinyes, or Furies, chthonic deities that avenge patricide and matricide. He, at the instigation of his sister Electra and the god Apollo, has killed their mother Clytemnestra, who had killed their father, King Agamemnon, who had killed his daughter and their sister, Iphigenia. Orestes finds a refuge and a solace at the new temple of Apollo in Delphi, and the god, unable to deliver him from the Erinyes' unappeasable wrath, sends him along to Athens under the protection of Hermes, while he casts a drowsy spell upon the pursuing Erinyes in order to delay them.
Clytemnestra's ghost appears from the woods and rouses the sleeping Erinyes, urging them to continue hunting Orestes. The Erinyes' first appearance on stage is haunting: they hum a tune in unison as they wake up, and seek to find the scent of blood that will lead them to Orestes' tracks. Ancient tradition says that on the play's premiere this struck so much fear and anguish in the audience, that a pregnant woman named Neaira suffered a miscarriage and died on the spot.
The Erinyes' tracking down of Orestes in Athens is equally haunting: Orestes has clasped Athena's small statue in supplication, and the Erinyes close in on him by smelling the blood of his slain mother in the air. Once they do see him, they can also see rivulets of blood soaking the earth beneath his footsteps.
As they surround him, Athena intervenes and brings in a jury of twelve Athenians to judge her supplicant. Apollo acts as attorney for Orestes, while the Erinyes act as advocates for the dead Clytemnestra. During the trial, Apollo convinces Athena that, in a marriage, the man is more important than the woman, by pointing out that Athena was born only of Zeus and without a mother (Zeus swallows Metis). Before the trial votes are counted, Athena votes in favour of Orestes. After being counted, the votes on each side are equal. Athena then persuades the Erinyes to accept her decision. They eventually submit. Athena then renames them Eumenides (The Kindly Ones), and they will now be honored by the citizens of Athens and ensure their prosperity. Athena also declares that henceforth hung juries should result in the defendant being acquitted, as mercy should always take precedence over harshness.
That the play ends on a happy note may surprise modern readers, to whom the word tragedy denotes a drama ending in misfortune. The word did not carry this meaning in ancient Athens, and many of the extant Greek tragedies end happily.
Worth noting here is the metaphorical aspect of this entire drama. Initially, in their role as avengers of bloodshed, the Erinyes are classical equivalents to the Code of Hammurabi and the Torah, which demand “an eye for an eye, a tooth for a tooth”. Thus, they initially embody the concept of lex talionis, or “law of retribution”.
The change from an archaic self-help justice by personal revenge to administration of justice by trial symbolises the passage from a primitive society governed by instincts, to a modern society governed by reason: justice is decided by a jury of peers, representing the citizen body and its values, and the gods themselves sanction this transition by taking part in the judicial procedure, arguing and voting on an equal footing with the mortals. This theme of the polis self-governed by consent through lawful institutions, as opposed to tribalism and superstition, recurs in Greek art and thought.
The dramatization of societal transformation in this myth (the transition to governance by laws) is both a boast and justification of the then relatively new judicial system. The concept of objective intervention by an impartial entity against which no vengeance could be taken (the state) marked the end of continuous cycles of bloodshed, a transition in Greek society reflected by the transition in their mythology--the Erinyes are a much greater part of older Greek myths than comparatively more recent ones. The reflection of societal struggles and social norms in mythology makes plays like these of special interest today, offering poignant cultural and historical insights.
“A part of the self” can also be interpreted more figuratively as a significant other, such as a spouse; thus, Clytemnestra’s feelings for Agamemnon are characterized as ‘philos-aphilos’ as well. As Richmond Lattimore defined it thus, “the hate gains intensity from the strength of the original love when that love has been stopped or rejected.” Clytemnestra’s love for Agamemnon has been quashed by his sacrifice of Iphigeneia and his return with Cassandra as a mistress. Likewise, Orestes’ sentiments toward his mother are intensified by anger at her murder of his father and resentment at the fact that she chose her lover over her children – essentially, they are “the price for which she bought herself this man.” These conflicting feelings are embodied in Clytemnestra’s dream about nursing the snake.
Lattimore also draws a parallel between the Oresteia and Hamlet, suggesting that the sensation of ‘philos-aphilos’ engendered by Prince Hamlet’s emotional connections to his mother, Queen Gertrude, and to Ophelia, who are both on the side of King Claudius – himself a close blood relative who might have held Hamlet’s affection and regard before usurping the throne – are what make the play a tragedy.