When Agamemnon, the king of Argos, returns home from the Trojan War, he is murdered in cold blood by his wife, Clytemnestra, and her lover, Aegisthus. Afterward, Aegisthus and Clytemnestra are married, and Aegisthus becomes king. Orestes, the young son of Agamemnon, is sent by a relative to Phocis before Aegisthus can destroy him. Electra, the daughter, remains, but is given in marriage to an old peasant, lest she marry a warrior powerful enough to avenge her father’s death.

One day, after Electra and the peasant go out to do the day’s work, Orestes comes in disguise with his best friend, Pylades, to the farm to seek Electra. They hear her singing a lament for her fate and for the death of her father. A messenger interrupts her lament with word that a festival is to be held in honor of the goddess Hera and that all Argive maidens are to attend. Electra says she prefers to remain on the farm away from the pitying eyes of the people of Argos. The messenger advises her to honor the gods and to ask their help. Electra mistakes Orestes and Pylades for friends of her brother. She tells them her story and speaks of her wish that Orestes will avenge the death of Agamemnon and the ill treatment of his children. Aegisthus, meanwhile, offers a reward for the death of Orestes.

The peasant returns from his work and asks Orestes and Pylades to remain as his guests. Electra sends her husband to bring the relative who took Orestes away from Argos. On his way to the peasant’s cottage, the old foster father notices that a sacrifice was made at the tomb of Agamemnon and that there are red hairs on the grave. He suggests to Electra that Orestes might be in the vicinity, but Electra answers that there is no chance of his being in Argos. When Orestes comes out of the cottage, the old man recognizes a scar on his forehead; thus brother and sister are made known to each other.

At the advice of the old peasant, Orestes plans to attend a sacrificial feast over which Aegisthus will preside. Electra sends her husband to tell Clytemnestra that she gave birth to a baby. Electra and Orestes invoke the aid of the gods in their venture to avenge the death of their father.

Orestes and Pylades are hailed by Aegisthus as they pass him in his garden. The pair tell Aegisthus that they are from Thessaly and are on their way to sacrifice to Zeus. Aegisthus informs them that he is preparing to sacrifice to the nymphs and invites them to tarry. At the sacrifice of a calf, Orestes plunges a cleaver into Aegisthus’s back while Aegisthus is examining the beast’s entrails. Orestes then reveals his identity to the servants, who cheer the son of their former master. Orestes carries the corpse of Aegisthus back to the cottage, where it is hidden after Electra reviles it.

At the sight of Clytemnestra approaching the peasant’s hut, Orestes has misgivings about the plan to murder her. He fears that matricide might bring the wrath of the gods upon him. Electra is, however, determined to complete the revenge. She reminds Orestes that an oracle told him to destroy Aegisthus and Clytemnestra.

Clytemnestra defends herself before Electra with the argument that Agamemnon sacrificed Iphegenia, their child, as an offering before the Trojan venture and that he returned to Argos with Cassandra, princess of Troy, as his concubine. Electra indicts her mother on several counts and claims that it is only just that she and Orestes murder her. The queen enters the hut to prepare a sacrifice for Electra’s supposed firstborn; within, Orestes kills her, though he moans in distress at the violence and bloodshed and matricide in which the gods involved him.

The Dioscuri, twin sons of Zeus and brothers of the half divine Clytemnestra, appear to the brother and sister, who are overcome with mixed feelings of hate, love, pride, and shame at what they did. The twin gods question Apollo’s wisdom, whose oracle advised this violent action; they decree that Orestes should give Electra to Pylades in marriage and that Orestes himself should be pursued by the Furies until such a time as he will face a trial in Athens, from which he will emerge a free man.