Before the play begins . . .
In the first play of the Oresteia trilogy, Agamemnon returns to Argos after ten years away at the Trojan War. His wife Clytemnestra, who has been ruling the kingdom in his absence, murders him and his concubine Cassandra. Clytemnestra’s reasons include jealousy, envy, and revenge for the sacrifice of their daughter Iphigeneia, whom Agamemnon killed in order to sail to Troy. Clytemnestra has also taken up with Agamemnon’s cousin Aegisthus, who did not go to Troy.
Clytemnestra and Agamemnon have two other children: daughter Electra, who has been in the court at Argos since before her father left; and son Orestes, who has grown up in the house of Strophios away from Argos.
As the play begins . . .
Orestes and his best friend Pylades arrive in Argos and pay their respects at the grave of Agamemnon. When Electra and a group of slave women (the Chorus) come to pour liquid offerings (libations) for Agamemnon’s grave, the two men withdraw to watch.
The women wonder about the efficacy of an offering sent by Clytemnestra, who murdered Agamemnon, but they begin nevertheless to pour the libations until Electra notices traces of someone else at the grave. Orestes comes forward, and a touching recognition scene ensues. After they catch up with one another, they pray together to their father and make a plan to avenge his death.
Orestes and Pylades gain admittance to the palace in disguise and report to Clytemnestra that Orestes is dead; she takes the news well. We meet Orestes’ nurse who really does grieve his “death,” and who has been sent to fetch Aegisthus. He returns to hear the good news and enters the palace only to be killed by Orestes. Clytemnestra, who now realizes that she has welcomed an avenging son home, appeals to him on the basis of her motherhood, and Orestes hesitates for a moment to kill her. Pylades reminds him of the orders of Apollo, and Orestes takes Clytemnestra back inside to die.
The doors open to reveal Clytemnestra and Aegisthus dead, with Orestes in triumph over them. (Much as Clytemnestra appeared over the bodies of Agamemnon and Cassandra in the previous play.) As the play ends, Orestes sees the Furies chasing him, and he flees toward Delphi to the protection of Apollo.
In the last play . . .
Orestes is in Delphi, where Apollo purifies him of the matricide, but the Furies continue to chase him. He goes to Athens, where he stands trial with Athena as judge, and he’s acquitted. Athena then domesticates the scary Furies into the nice Eumenides.