Orestes, and the Old Man, Orestes's tutor, arrive at Mycenae at daybreak. They have come to exact revenge for the murder of Agamemnon, Orestes's father, as instructed by an oracle of Apollo.
Electra emerges from inside the palace gates, pouring forth her grief in a mournful address to the heavens and praying to the deities to help her exact revenge for her father's death.
The chorus, which is comprised of the virgins of the palace, attempt to console Electra
But Electra, bemoaning the oppression she suffers at her mother's hands, her deep sorrow at her father's death, and her longing for Orestes' return, proves inconsolable.
Chrysothemis, Electra's younger sister, emerges from the palace with a funeral offering.She warns Electra that Aegisthus intends to lock her away in a secluded room unless she pulls herself together.
Clytemnestra approaches and chastises Electra for mourning in the streets, and the two have an argument about Agamemnon's murder. Clytemnestra maintains that it was a just murder, done as revenge.
Electra holds that the sacrifice was necessary, and that, regardless of this detail, Clytemnestra murdered Agamemnon out of lust for Aegisthus.
The Old Man enters in the character of a Phocian, bearing a false account of Orestes's death. Clytemnestra is briefly touched by maternal feelings, yet delighted that her prayer has been answered.
Electra is overcome with grief.
Chrysothemis returns from Agamemnon's grave, full of joy and sure that Orestes has returned. Electra informs her sister that, to the contrary, Orestes is dead.
Orestes then approaches with Pylades in the character of a Phocian, carrying an urn that, it is pretended, contains Orestes' ashes. Electra's despair is heightened, and she takes the urn and laments over it at length.
Orestes, visibly affected by the sight of his sister's suffering, reveals himself to her, displaying their father's ring as proof of his identity. Electra's grief is immediately replaced with joy.
Aegisthus approaches and asks Electra where the Phocians with news of Orestes's death have gone, and she points inside the house. He demands that the doors and gates of the palace be opened, so that the citizens can see what he thinks is Orestes's corpse.
Orestes brings the corpse of Clytemnestra, covered with a sheet, to Aegisthus. when the body is uncovered, Aegisthus realizes that he has been trapped and that death is upon him. Orestes orders Aegisthus inside so that he might kill him in the exact spot where, years before, Aegisthus killed Agamemnon.
Electra has her revenge.