For ten long years, the Greek army has been fighting at Troy. The war began after the Trojan prince Paris was promised that he would marry the prettiest woman in the world after he judged Aphrodite to be the winner in a divine beauty contest. However, Helen was already married to the Spartan King Menelaus, who appealed to his brother Agamemnon for help, and the two assembled a massive army to attack Troy and rescue Helen. During these ten years, many wives have waited expectantly to hear from their husbands, and many cities have been left without a king. In Argos, Agamemnon's wife Clytaemnestra has ruled the city in his absence, holding within her heart a secret hatred, because he sacrificed their eldest daughter at Aulis so that the Greek fleet could sail to Troy. Clytaemnestra has a new lover, Aegisthus, and together the two have plotted to murder Agamemnon when he returns from Troy.
The story opens as, at long last, a signal fire burns within sight of Argos, meaning that the war has ended and the Greeks are coming home. Clytaemnestra keeps her murder plot a secret and acts very excited when she hears this news, telling the Chorus of Elders that she has missed her husband so very much during all these years. A Herald soon arrives to announce that Agamemnon's ship has landed and that he will be coming into the city. When the King of Argos himself appears soon after in his chariot, his wife acts very pleased to see him, and lies by saying that she has had no other lovers while he was away. The deceitful woman urges him to walk across a red carpet of honor, because he has lead the Greeks to victory. The man does not want to offend the gods by this arrogance, but Clytaemnestra finally convinces him to do as she wishes, after which the two enter the palace of Argos together.
Meanwhile, a captive Trojan princess named Cassandra remains in the chariot, lamenting about how Clytaemnestra is going to murder Agamemnon and herself. No one believes these words, however. The young woman curses Apollo for not saving her from death and boldly walks out of the chariot into the royal palace, knowing that she is going to die. The Chorus of Elder becomes alarmed when they hear screams of pain coming from within the palace. The doors open, and Agamemnon's bloody body lies on the ground beside that of Cassandra, while Clytaemnestra stands above them, showing her true personality now. She rants about how he has been punished for the death of her eldest daughter Iphigenia, and also for being unfaithful to her by making Cassandra his love slave. Aegisthus emerges from within the palace also, declaring that he has revenge for the death of his siblings, killed by Agamemnon's father Atreus.
Yet the Chorus of Elders does nothing to stop Clyatemnestra and merely cowers in fear at what has happened. They call Aegisthus a coward, since it was a woman and not a man who committed these two murders, and he in turn argues back. Tired, Clytaemnestra urges Aegisthus to go back into the royal palace at Argos with her, declaring that they will now rule Argos together. She adds that they will bury Agamemnon themselves so that his bloody body does not stay there in the palace. The woman remains peaceful because, after ten years, vengeance has been exacted against her husband. Agamemnon chose to be a soldier first and a father second, sacrificing his own daughter so that the Greek fleet could sail to Troy, wreaking more havoc and destruction. The mother's anger festered until it was released upon his return home. With these words said, the two reenter the palace and close the doors behind them.
