Knowledge of the Curse on the House of Atreus and the events of Agamemnon is essential for understanding the events of The Libation Bearers. For a more detailed look, see the ClassicNote on Agamemnon. The Curse on the House of Atreus began with a feud between two brothers, Atreus and Thyestes. Thyestes was forced to flee. He made overtures of peace to his Atreus, returning with his children, and Atreus pretended to be appeased. He invited Thyestes to a feast, but he secretly slaughtered all of Thyestes' children and served them to Thyestes in a manner that disguised the true nature of the meat. Thyestes unwittingly ate his own children. At the end of the meal, Atreus revealed to Thyestes what he had been eating, and Thyestes called down a Curse on Atreus' house. Thyestes fled with his one surviving child, Aegisthus. Atreus had two sons, Agamemnon and Menelaus. Agamemnon married Clytaemestra, and Menelaus married Helen. Helen was seduced by Paris of Troy, and she went willingly with him back to his city. Agamemnon and Menelaus organized the chieftains of Greece into a massive force to win her back. The fleet converged at Aulis, but was unable to set sail because the goddess Artemis was angry and kept the weather against them. The prophet Calchas told Agamemnon that to appease the goddess, the king would have to sacrifice his own daughter, Iphigeneia. Agamemnon did so, and he and his troops set sail. They waged war on Troy for ten long years, finally destroying the city and butchering or enslaving all of the people there. On the return voyage, Agamemnon's contingent passed through a terrible sea storm, and only Agamemnon's ship survived.
Agamemnon returned with a captive mistress, the prophetess Cassandra. While he had been away, his wife Clytaemestra had taken a lover. This lover was none other than Aegisthus, the sole surviving son of Thyestes. Soon after Agamemnon's return, Clytaemestra murdered the king while he bathed. Cassandra was the next victim; the prophetess, convinced that she could not change her fate, walked knowingly towards her own death. Clytaemestra displayed the body of the king and proclaimed that justice had been done. Her motivations were mixed and included a desire for power and her love for Aegisthus, but the queen was also taking revenge for Agamemnon's slaughter of their innocent daughter. Clytaemestra and Aegisthus installed themselves as the unlawful rulers of Argos. Which brings us to The Libation Bearers.
Set in Argos, many years after the death of Agamemnon, the play opens with the return of Orestes, accompanied by his friend Pylades. Orestes and his sister Electra are now young adults, but they have been deprived of their rightful inheritance. Orestes has been living in exile, and Electra has been made into a servant in her own house. Orestes, disguised, pays respects at the tomb of his father. While he is there, a group of women, led by Electra, comes to the grave with shows of mourning. Orestes hides himself so that he can learn the intent of the women. The women pour libations in homage to the dead, but Electra is stunned to find a lock of hair on the tomb. The lock of hair is a traditional offering to the dead, and this lock is special: it has color and texture unique to the children of Agememnon, and so it must have come from the head of Orestes. Orestes reveals himself, and proclaims that he has returned to avenge his father and reclaim the throne; Apollo himself has commanded that Orestes kill the usurpers. Orestes and Electra try to invoke the spirit of Agamemnon, working themselves into a frenzy so that Orestes will be able to go through with the act of matricide.
Orestes asks the Chorus why they have come to make offerings at Agamemnon's tomb. The slave women tell him that Clytaemestra sent them; she has had terrible nightmares about being bitten by a serpent that she was breastfeeding. The soothsayers have interpreted her dreams as meaning that the dead are angry, and Clytaemestra sent Electra and the slave women to pour offerings at Agamemnon's tomb in an attempt to appease his ghost.
Orestes makes a plan: he and Pylades, disguised, will gain entry into the palace. Electra will keep watch, and the Chorus of slave women will keep quiet but help if they can. The two men will wait for an opportune moment to slay Clytaemestra and Aegisthus.
There is a scene change from the tomb of Agamemnon to just outside the palace of Clytaemestra. Orestes and Pylades approach the doors to the palace and pretend to be foreign travelers bringing terrible news: Orestes is dead. Clytaemestra welcomes them; she then sends for Aegisthus so that he can hear the important news. Cilissa, Orestes' old nurse, goes to fetch him. She weeps as she goes, saddened because Orestes was like a son to her. The Chorus hints that Orestes may still be alive, and they urge Cilissa to tell Aegisthus to come alone, without his bodyguards. Cilissa does not entirely understand the Chorus' cryptic instructions, but she does as they ask. Aegisthus returns unguarded. He goes into the palace, and moments later one of his followers emerges and announces that Aegisthus has been killed. The follower finds and warns Clytaemestra. Before she can take measures to protect herself, Orestes and Pylades come out of the palace and seize her. Orestes has a moment of indecision, but Pylades convinces him that he must go through with the act. Clytaemestra tries unsuccessfully to get him to spare her life, finally warning him that if he kills her he will be cursed. Orestes is not swayed, and he and Pylades drag the queen inside the palace.
The palace doors open, revealing Orestes with the bodies of his mother and Aegisthus. He proclaims that justice has been served, and justifies his actions. He announces his intent to go to the shrine of Apollo and await further instructions. Suddenly, the Furies appear. They are visible to Orestes only. Fearsome goddesses with snakes for hair, they have come to make Orestes pay for murdering his mother. Orestes flees, pursued by the monsters, and the Chorus wonders if the Curse on the House of Atreus will ever be purged.