Poseidon is lamenting the fall of Troy. Athena joins him; though she was on the side of the Achaeans, who attacked Troy to procure Helen, she is incensed over the Greeks’ exonerating Ajax from sexually assaulting Trojan princess Kassandra at Athena's temple. She believes that they are extremely disrespectful to her. Athena and Poseidon devise a plan to carry out revenge on the Greeks by destroying the Greek ships during their return voyage. Queen Hecuba of Troy—Kassandra's mother—has been dethroned, and as she languishes in a Greek camp, she laments the loss of her husband Priam, her children, and her city. She curses Helen for starting the war with the Greeks that put her in this terrible situation.
A Greek herald, Talthybius, tells Hecuba what is going to happen to her and her family: Hecuba is to be taken by the loathsome General Odysseus and put to work as his slave; her daughter Kassandra will become General Agamemnon's concubine even though she is a virgin priestess of Apollo; and her daughter Polyxena, he cryptically tells her, is happy somewhere.
Kassandra appears. She has been driven almost insane by a curse that gives her the gift of seeing the future, but nobody believes her when she tells them. Because of her prophetic gift, she knows that when she arrives in Argos, Agamemnon's wife will be so angry with both her husband and his new concubine that she will kill both of them. She also speaks of Odysseus’s wanderings and harsh fate, but again, no one believes her.
Andromache, Hecuba's daughter-in-law, arrives on a Greek wagon of spoils of war with her baby son Astyanax to share the news that Hecuba's youngest daughter Polyxena has been killed as a sacrifice at the tomb of Achilles, and Andromache is to become the concubine to Achilles' son, Neoptolemus. Hecuba feels that she should oblige her new master so that he will allow her to raise her son to become the future savior of Troy, but the Greeks have no intention of allowing this to happen. Talthybios grimly and matter-of-factly tells the grieving mother and grandmother that, at Odysseus’s urging, the Greeks intend to throw the newborn from the battlements of Troy to kill him, avoiding the risk his growing up and seeking revenge. If Andromache avenges him by throwing a curse on the home-going Greek ships, her son will not be given a proper burial. She is taken away after her son is ripped away from her and taken to his death.
Menelaus, the king of Sparta, is angry because his purpose in coming to Troy was to take his revenge on Paris, but now he discovers that he is charged with the job of taking Helen back to Greece with him because there is a death warrant for her there. Helen is brought before him, and she is still a bewitching beauty even after all that has transpired in the conflict. Menelaus does not want her to speak, but Hecuba suggests he let her, if only so that Hecuba can respond and refute Helen’s words. Menelaus agrees.
Helen pleads with Menelaus to spare her life, telling him that she was under the spell of the goddess Aphrodite/Kypris and that she fully intended to return to Menelaus before being spellbound. Hecuba is actually to blame, she adds, for giving birth to Paris and not killing him even after she had a dream that this son of hers was a firebrand and thus dangerous.
Hecuba scoffs at this story and warns Menelaus that Helen will betray him again. He remains resolute and makes sure that Helen goes back to Greece on a different ship than he does.
Talthybius returns with the body of new-born Astyanax resting on Hector's shield. It has been Andromache's wish that she bury her child herself in accordance with Trojan burying rituals, but her ship has already sailed and so it is Hecuba's task to prepare the child for his burial. This is too much for Hecuba. As flames rise from the ruins of Troy, Hecuba makes an attempt on her own life by trying to throw herself into the fire, but she is restrained by guards and is put on a ship with the Trojan women who remain with her, sailing towards their Greek conquerors.
