As Orestes, Pylades, and an old slave arrive before the palace of Mycenae, the old slave points to the city and tells the story of how Orestes left it long ago. Orestes’s father, Agamemnon, was murdered years ago, and Orestes’s sister, Electra, gave the infant Orestes to the old slave. The old slave cared for Orestes as if he were his own son and raised him to seek revenge for his father’s death. Now, the old slave says, it’s finally time for Orestes to take action. Orestes has a plan: before traveling to Mycenae, he visited the Delphic oracle, who spoke the words of Apollo. “By lone deceit and stealthy craft / Must blood be shed and victory won,” the oracle said. The old slave will go to the palace, Orestes says, because the old slave’s age will make him unrecognizable, and tell the people there that Orestes has been killed in a chariot accident during the Pythian Games. The slave will also take along a bronze urn and claim it holds Orestes’s cremated remains. Suddenly, the sound of a woman weeping comes from inside the palace. The old slave wonders if it is Electra and suggests they stop and listen, but Orestes insists that their first stop has to be Agamemnon’s grave.
As Orestes heads for Agamemnon’s grave with Pylades and the old slave, Electra comes out of the palace. She has been grieving night and day since her mother, Clytemnestra, and her mother’s husband, Aegisthus, murdered her father. Electra says that she is like the nightingale and that she will never stop weeping with sorrow. She prays to the gods that “the dread Furies” will punish Agamemnon’s murderers and that her brother, Orestes, will return. As Electra mourns, a chorus of Mycenean women arrive to comfort her. They ask what good it will do keep mourning, since doing so won’t bring Agamemnon back to life, but Electra insists that doing so is necessary because it’s a child’s duty to remember a deceased parent. Plus, Electra is forced to live with her father’s killers, and they abuse her and treat her like a slave. As Electra mourns, her sister, Chrysothemis approaches and urges her to give up her useless anger. Chrysothemis despises Clytemnestra and Aegisthus too, but angering them with public lamentations for Agamemnon does more harm than good. She tells Electra that Aegisthus is planning to bury Electra alive in a cave if she doesn’t stop her public cries, but Electra is unmoved, saying that she’ll do anything to honor her father’s memory.
According to Chrysothemis, Clytemnestra had a dream in which Agamemnon was alive. He struck the hearth with his staff and a large tree branch grew that covered all of Mycenae. Clytemnestra was scared by the dream and ordered Chrysothemis to bring libations to Agamemnon’s grave, but Electra says that doing so would be wrong. She tells her sister to bury the offerings, far away from their father’s grave. As Chrysothemis goes to bury the offerings, the chorus implies that it must have been “Justice” that sent the nightmare to Clytemnestra. Suddenly, Clytemnestra approaches on her way to give offerings to the gods and scolds Electra for her misbehavior. She knows Electra hates her because she killed Agamemnon, but Clytemnestra cares very little. Agamemnon had sacrificed their daughter, Iphigenia, to the goddess Artemis, and when Clytemnestra killed him to avenge her daughter, she was on what she calls “the side of Justice.”
Electra claims that Agamemnon killed a stag in Artemis’s “sacred grove” and boasted unwisely, and so he had to sacrifice Iphigenia to appease the goddess. Besides, Electra says, Clytemnestra didn’t kill Agamemnon just to avenge Iphigenia; she did it because of her lust for Aegisthus and her desire to rule Mycenae without Agamemnon. According to Electra, it doesn’t matter if justice was on Clytemnestra’s side, because there cannot be a “more shameful” act than murder. Clytemnestra offers a prayer to Apollo that evil will strike her enemies and that she may be able to continue living in luxury with her children who do not hate her. Suddenly, the old slave arrives, claiming to be a messenger from Phocis. He claims that Orestes has been killed in a tragic chariot accident. Electra is devastated, exclaiming that if Orestes is dead, she might as well be dead too.
As Clytemnestra invites the old slave inside, she tells him that nothing can make a mother hate her own child. Electra remains outside the palace, wailing, and Chrysothemis excitedly runs back to her. She has been to Agamemnon’s grave and there are fresh libations there. Orestes must be back, she says. However, Electra tells her sister that Orestes is dead, and whoever put fresh offerings on Agamemnon’s grave must have done so in memory of Orestes. They have no friends and Orestes isn’t coming back, Electra says, so they must kill Aegisthus themselves. Chrysothemis accuses Electra of going mad, saying that Electra is a woman, not a man, and she couldn’t possibly kill Aegisthus. Electra maintains that giving up is impossible, but Chrysothemis feels that they have no chance of winning.
As Chrysothemis goes back into the palace, Orestes approaches with Pylades, holding the bronze urn, and asks Electra where Aegisthus’s house is. Electra asks him if he carries the urn containing Orestes’s remains, and he confirms he is. Electra speaks mournfully to the urn, cradling it, but Orestes surprises her by saying that she shouldn’t be sad; Orestes isn’t actually in the urn. He reveals that he is alive by showing Electra a ring bearing Agamemnon’s seal, and they embrace. She begins to rejoice but he tells her it is not yet time to celebrate. The old slave comes out of the palace and reports that Clytemnestra is alone. It is time. They all go into the palace, leaving the chorus outside.
Electra soon comes back outside. She says that she is looking out for Aegisthus to arrive so that he does not catch them by surprise. “My son, my son! Have mercy on your mother!” Clytemnestra cries from inside the palace, and Electra yells back, urging Orestes to strike Clytemnestra again. Orestes, Pylades, and the old slave exit the palace with blood on their hands, and Orestes tells Electra that “all is well” inside the palace. The chorus sees Aegisthus approaching in the distance, and they urge the men to go back inside before they are discovered. “I can look after everything here,” Electra says, and the men slip quietly into the palace.
As Aegisthus approaches, he immediately tells Electra that he has heard of Orestes’s death and asks where the messengers who brought the news are. Electra tells him that they’re inside with Clytemnestra and that they’ve “won their way to her heart.” Aegisthus orders the palace doors opened so that all the people of Mycenae may see the remains of Orestes. As the palace doors open, Orestes exits carrying the body of Clytemnestra covered by a shroud, and as Aegisthus begins to remove the shroud to examine the body, he tells Electra to go find Clytemnestra. “No need to look,” Electra says. “She’s here already.” Aegisthus begins to scream, realizing that he’s trapped. Orestes reveals his identity as Agamemnon’s son and orders Aegisthus into the palace. Aegisthus begs Orestes for a word of defense, but Electra cuts him off, telling Orestes to kill Aegisthus right away and leave his body for “the dogs and birds.” Orestes leads Aegisthus into the castle, to the exact place where Aegisthus killed Agamemnon many years before. Electra stays outside with the chorus, who celebrate the end of Electra’s long suffering.