At early dawn, before a desolate mountain hut, a peasant is hailing the new day and bemoaning the plight of his young wife, Electra, banished daughter of the dead warrior, King Agamemnon, and his Queen, Clytemnestra.
In his reverie he recalls the triumphant return of Agamemnon after the conquest of Priam, only to be murdered by his wife and her lover, Aegisthus, who now rule Argos and Mycenae. Orestes, Agamemnon's son, was saved from a like death by an old friend of the slain King, and was given into the care of King Strophio in Phocis; but Electra suffered a harsher fate: because Aegisthus feared she might have a child, sired by some powerful house, to avenge her father if she were allowed to wed in her own class, he sought first to kill her, too, but was dissuaded by Clytemnestra. He decreed, however, that she must marry this poor peasant and thus remain powerless to menace his rule. The peasant has left Electra virgin, since he feels himself unworthy of a princess.
Electra, appearing, herself cries out in bitterness at her lot, calling curses upon her mother. The peasant then chides her for toiling, but she voices her thanks to him for his kindness and tells him of her determination to make his home bright. As he goes to his work and she to the spring for water, two armed men enter--Orestes, her brother, and his friend, Pylades, son of Strophio.
Orestes tells Pylades that, come to avenge his father, he has just offered sacrifice of his tears and tresses and a black lamb upon his father's grave. He plans to lurk in the mountains to await his chance for revenge, meanwhile searching for his sister, of whose humiliation he has heard. As they speak, Electra approaches; Orestes, deeming her only a farm maid, plans to question her. She cries out her grief as Agamemnon's daughter, and her brother remains silent as a chorus of women of Argos appear in festal dress to ask her to lead in the morrow's rites. She replies that she cannot while her mother lies in the usurper's arms "and blood is about her bed."
Orestes now comes from concealment. Electra does not recognize him as he cautiously tells her that he brings word of her brother--that Orestes seeks word of her. She tells him of her life with the peasant and he, to test her, asks if she would be willing to aid her brother in the slaying of her mother for revenge. Yes, she replies--with the same ax that slew her father.
The peasant returns and is bidden by Electra to hasten to the old friend of her father, now in exile as a herdsman, that he may come to hear the news of Orestes whom he rescued. She bids him bring meat to help make the strangers welcome. The peasant soon returns with the old man who, having noted the sacrifice upon Agamemnon's grave, has suspected the return of Orestes. He recognizes the grown Prince by a scar upon his brow. Her brother is made known to Electra and they embrace.
The talk is now of revenge, and the old man, demanding that Orestes strike down both Aegisthus and his mother, tells the Prince that Aegisthus is, at that very moment, in a nearby pasture preparing a wreathed ox for sacrifice, guarded only by a few of his servants. Orestes asks how he may lure his mother forth as well, but Electra demands the doing of this deed. She bids the old man tell Clytemnestra that she has borne a son, news which will bring the Queen to the hut. Orestes sets forth, and Electra waits with a sword--ready to kill herself should her brother fail.
Soon a messenger appears with word that Aegisthus is dead. The usurper hailed Orestes and his men as they approached, and, unaware of their errand, invited them to share in the sacrificial rite. Orestes stripped the limbs of the ox, but omens of doom at Orestes' hands startled the King. While Aegisthus studied the animal, Orestes brought his sword down upon his foe and Aegisthus fell dead. The young Prince then identified himself to the servants and was hailed as a deliverer.
Orestes and his men arrive with the body of Aegisthus. Electra curses the body and it is then hidden in the hut to await the coming of Clytemnestra whose chariot is approaching. Orestes shrinks from the thought of killing his own mother, but, scorned by Electra as a coward who fears to avenge his father, he agrees to strike the same stealthy blow that killed Agamemnon. He goes to hide himself in the hut.
Clytemnestra arrives, accompanied by her handmaidens. When Electra reproaches her for her exile, she lays the blame for her misdeeds on Agamemnon. Clytemnestra goes into the hut, followed by Electra, to bless her grandchild. Her death cry is heard: "O children, children: in the name of God, slay not your mother!" Then her body and that of Aegisthus are borne from the house. Orestes comes forth, lamenting the sin of having killed his mother, but Electra declares hers the blame.
In their surpassing grief, they tell of the tragedy they have just caused. Orestes cries out at the memory of his mother, her raiment bloodied, baring her bosom and falling to her knees. Electra tells that her mother touched her cheek and moaned, "Mercy, my child, my own!" Electra, in pity, dropped the sword, but Orestes, blinding his eyes with his mantle, struck the death blow, the sword finding his mother's throat. But Electra says, "I gave thee the sign and the word, I touched with mine hand thy sword." The two kneel together and cover their mother's body with raiment.
In the sky there appears a vision of Castor and Polydeuces. They declare the Queen's doom a righteous one, but not the deed itself. They ordain that Electra shall become the wife of Pylades in exile, and say that Orestes must flee from Argos to Athens where, at length, Phoebus shall take the stain of murder upon his own head, allowing the Prince to at last find happiness after penance. The brother and sister, so briefly reunited, say farewell to each other and to Argos.