Orestes, the grown son of Agamemnon and Clytemnestra, and his companion, Pylades, travel to Argos, hoping for revenge, and end up at the house of Electra and her husband. They have concealed their identities in order to get information, claiming that they are messengers from Orestes, but the aged servant who smuggled Orestes off to Phocis years before recognizes him by a scar, and the siblings are reunited. Electra is eager to help her brother in bringing down Clytemnestra and Aegisthus, and they conspire together.
While the old servant goes to lure Clytemnestra to Electra's house by telling her that her daughter has had a baby, Orestes sets off and kills Aegisthus and returns with the body. His resolve begins to waver at the prospect of matricide but Electra coaxes him into going through with it. When Clytemnestra arrives, he and Electra kill her by pushing a sword down her throat (which is only recounted and not shown), leaving both feeling oppressive guilt. At the end, Clytemnestra's deified brothers Castor and Polydeuces appear. They tell Electra and Orestes that their mother received just punishment but that their matricide was still a shameful act, and they instruct the siblings on what they must do to atone and purge their souls of the crime.