Orestes and The Tutor arrive in the city of Argos. The Tutor complains that the city is unpleasant and that the Argives are unfriendly, but Orestes says that he was born there. Jupiter approaches them disguised as a man and tells them the history of Argos: fifteen years ago, Queen Clytemnestra and the present King Aegistheus murdered Agamemnon, the old king and Clytemnestra's husband. The Argives all knew what would happen but did not try to prevent it. Instead of punishing them, the gods sent flies to torment the city. Since the murder, the Argives have been living in remorse, attempting to atone for their sins.
Jupiter mentions that Agamemnon had a son named Orestes, and expresses the hope that if Orestes ever came back to Argos he would not interfere with the remorse of its people, since this remorse pleases the gods. When Jupiter departs, Orestes complains to his Tutor that he feels he does not belong anywhere. He has no true home and no true family. He wishes he could somehow belong to his birthplace, Argos.
Electra appears and curses the statue of Jupiter in the square. She expresses her hope that her brother Orestes will one day come to avenge his father's death and free Argos. Orestes introduces himself to her as Philebus. She tells him that her mother has made her into a servant and that she hates the king and queen. Orestes tells her that outside Argos people can live happily without remorse.
Queen Clytemnestra appears and tells Electra that she must come to the annual Dead Man's Day ceremony. Electra explains to Orestes that on this day the dead are let out of a huge cave so they can torture the city for a whole day, avenging the sins that the living have committed. Electra and her mother quarrel, but finally Electra agrees to come to the ceremony. She asks Orestes to stay long enough to see it. Clytemnestra asks Orestes to leave Argos because his presence is upsetting Electra and threatens to bring disaster. Orestes decides to stay for the ceremony.
Accompanied by Jupiter, Orestes comes to the ceremony. The Argives publicly announce their sins and scream in fear about how the dead will torture them. Aegistheus tells the guards to find Electra, but they cannot locate her. He begins the ceremony, reminding the Argives of their sins. The cave is opened and the dead are set free. Suddenly Electra appears, dressed in white. The people rebuke her for disrespecting the dead, but she begins to dance, telling the Argives that people in other towns live happily with no remorse, and the dead would prefer to see the living be happy, not remorseful.
When the Argives begin to listen to Electra, Jupiter causes a large stone to roll away from the cave. Terrified, the people curse Electra for tempting them. Aegistheus orders her to leave Argos forever. Once the others have left, Orestes approaches Electra to convince her to leave with him. She tells him that she must stay in Argos because she is waiting for her brother to come and she must remain there to help him carry out his revenge. Orestes reveals his identity to her. Electra is shocked because she was expecting him to be a warrior.
Even though she now knows that Orestes is not a warrior who can help her with her revenge, Electra tells him to leave and says that she must stay behind. Orestes asks Zeus for a sign that he really should leave Argos like a coward. Jupiter causes light to flash around the stone. Suddenly, Orestes realizes that he must stay and free the people of Argos. He will not obey the orders of the gods. Realizing at last that this really is her brother who she thinks has come to help her kill the king and queen, Electra agrees to join him.
Jupiter enters the palace and orders Aegistheus to arrest Orestes and Electra immediately. Aegistheus refuses, saying that he is tired of putting on a false pretense for his subjects and would rather die than go on. Jupiter tells him that Orestes is dangerous: he knows he is free, and this could upset the entire order that Aegistheus has been building in Argos. As soon as Jupiter leaves, Orestes and Electra spring out from their hiding place and Orestes kills Aegistheus. Electra loses her nerve and tries to stop him there, but Orestes brushes her off and goes on to kill Clytemnestra. The siblings decide to hide in the shrine of Apollo for the night, but Electra realizes that the flies around them have turned into The Furies, the goddesses of remorse.
Orestes and Electra wake up in the shrine the next morning, and Electra is horrified at what has happened. She rejects Orestes, saying that he has brought guilt on her through his violence. The Furies egg her on, and Electra gives herself over to their tortures in order to escape her guilt. Jupiter enters, promising the siblings that he will give them salvation and the throne of Argos if they repent of their crime. Orestes refuses.
Jupiter tells Orestes that he is completely alone and that he has violated the laws of the gods. Orestes responds that he is free and that he can follow only his own laws, even if it means that he must be alone forever. Jupiter departs, saying that he pities him even though Orestes threatens his order. Electra spurns Orestes and runs after Jupiter. Completely alone, Orestes speaks to the Argives who have gathered outside to kill him. He tells them that he is Orestes, their rightful king, and that he has come to free them from the flies and their remorse. He has taken their sins upon himself and they must now learn to create their lives in freedom. He leaves the city and the Furies follow him.