Greek audiences would have known the story of the ill-fated marriage between Jason, hero of the Golden Fleece, and Medea, barbarian witch and princess of Colchis. The modern reader, to fully understand the events of Medea, needs to be familiar with the legends and myths on which the play is based.
Medea was of a people at the far edge of the Black Sea; for the Greeks of Euripides' time, this was the edge of the known world. She was a powerful sorceress, princess of Colchis, and a granddaughter of the sun god Helias. Jason, a great Greek hero and captain of the Argonauts, led his crew to Colchis in search of the Golden Fleece. King Aeetes, lord of Colchis and Medea's father, kept the Fleece under guard. A sorcerer himself, he was a formidable opponent. This legend takes place quite early in the chronology of Greek myth. The story is set after the ascent of Zeus, King of the gods, but is still near the beginning of his reign; Helias, the ancient sun god before Apollo's coming, is Medea's grandfather. Jason's voyage with the Argonauts predates the Trojan War, and represents the first naval assault by the Greeks against an Eastern people.
The traps set by Aeetes made the Golden Fleece all but impossible to obtain. By Medea's aid, Jason overcame these obstacles, and Medea herself killed the giant serpent that guarded the Fleece. Then, to buy time during their escape, Medea killed her own brother and tossed the pieces of his corpse behind the Argo as they sailed for Greece. Her father, grief-stricken by his son's death and his daughter's treachery, had to slow his pursuit of the Argo so he could collect the pieces of his son's body for burial.
Medea and Jason returned to his hereditary kingdom of Iolcus. Jason's father had died, and his uncle Pelias sat, without right, on the throne. Medea, to help Jason, convinced Pelias' daughters that she knew a way to restore the old king's youth. He would have to be killed, cut into pieces, and then put together and restored to youth by Medea's magic. The unwitting daughters did as Medea asked, but the sorceress then explained that she couldn't really bring Pelias back to life. Rather than win Jason his throne, this move forced Jason, Medea, and their children into exile. Finally, they settled in Corinth, where Jason eventually took a new bride.
The action of the play begins here, soon after Medea learns of Jason's treachery.
A Nurse enters, speaking of the sorrows facing Medea's family. She is joined by the Tutor and the children; they discuss Jason's betrayal of Medea. The Nurse fears for everyone's safety: she knows the violence of Medea's heart. The Tutor brings the children back into the house. The Chorus of Corinthian women enters, full of sympathy for Medea. They ask the Nurse to bring Medea out so that they might comfort her; the unfortunate woman's cries can be heard even outside the house. The Nurse complies. Medea emerges from her home, bewailing the harshness with which Fate handles women. She announces her intention to seek revenge. She asks the Chorus, as follow women, to aid her by keeping silent. The Chorus vows.
Creon (not to be confused with the Creon of Sophocles' Theban cycle), king of Corinth and Jason's new father-in-law, enters and tells Medea that she is banished. She and her children must leave Corinth immediately. Medea begs for mercy, and she is granted a reprieve of one day. The old king leaves, and Medea tells the Chorus that one day is all she needs to get her revenge.
Jason enters, condescending and smug. He scolds Medea for her loose tongue, telling her that her exile is her own fault. Husband and wife bicker bitterly, Medea accusing Jason of cowardice, reminding him of all that she has done for him, and condemning him for his faithlessness. Jason rationalizes all of his actions, with neatly enumerated arguments. Although he seems to have convinced himself, to most audience members Jason comes off as smug and spineless. He offers Medea money and aid in her exile, but she proudly refuses. Jason exits.
Aegeus, king of Athens and old friend of Medea's, enters. Aegeus is childless. Medea tells him of her problems, and asks for safe haven in Athens. She offers to help him to have a child; she has thorough knowledge of drugs and medicines. Aegeus eagerly agrees. If Medea can reach Athens, he will protect her. Medea makes the old king vow by all the gods.
With her security certain, Medea tells the Chorus of her plans. She will kill Jason's new bride and father-in-law by the aid of poisoned gifts. To make her revenge complete, she will kill her children to wound Jason and to protect them from counter-revenge by Creon's allies and friends. Many scholars now believe that the murder of Medea's children was Euripides' addition to the myth; in older versions, the children were killed by Creon's friends in revenge for the death of the king and princess. The Chorus begs Medea to reconsider these plans, but Medea insists that her revenge must be complete.
Jason enters again, and Medea adapts a conciliatory tone. She begs him to allow the children to stay in Corinth. She also has the children bring gifts to the Corinthian princess. Jason is pleased by this change of heart.
The Tutor soon returns with the children, telling Medea that the gifts have been received. Medea then waits anxiously for news from the palace. She speaks lovingly to her children, in a scene that is both moving and chilling, even as she steels herself so that she can kill them. She has a moment of hesitation, but she overcomes it. There is no room for compromise.
A messenger comes bringing the awaited news. The poisoned dress and diadem have worked: the princess is dead. When Creon saw his daughter's corpse, he embraced her body. The poison then worked against him. The deaths were brutal and terrifying. Both daughter and father died in excruciating pain, and the bodies were barely recognizable.
Medea now prepares to kill her children. She rushes into the house with a shriek. We hear the children's screams from inside the house; the Chorus considers interfering, but in the end does nothing.
Jason re-enters with soldiers. He fears for the children's safety, because he knows Creon's friends will seek revenge; he has come to take the children under guard. The Chorus sorrowfully informs Jason that his children are dead. Jason now orders his guards to break the doors down, so that he can take his revenge against his wife for these atrocities.
Medea appears above the palace, in a chariot drawn by dragons. She has the children's corpses with her. She mocks Jason pitilessly, foretelling an embarrassing death for him; she also refuses to give him the bodies. Jason bickers with his wife one last time, each blaming the other for what has happened. There is nothing Jason can do; with the aid of her chariot, Medea will escape to Athens. The Chorus closes the play, musing on the terrible unpredictability of fate.