Medea opens with a highly partial description of the circumstances from the nurse. She says that Jason has betrayed both Medea and his children and that Medea has reminded him of his promises to no avail. Now she lies wasting away in tears because of her husband’s cruel mistreatment.

Medea then puts her case directly to the women of Corinth. She says that the man who was all the world to her has turned out to be a villain and solicits their sympathy on the basis that they too may have been mistreated in marriage. The chorus promises that they will not prevent her from taking a just revenge.

Following this address, Medea has three male visitors, Creon, Jason and Aegeus, each of whom adds to the sympathy we have for her. Creon seems craven and harsh in his manner and in his banishment of the wronged woman. Aegeus (who is, of course, Athenian, like the audience) is the only man in the play who listens to Medea and treats her with respect. The most sympathy, however, is created by the cynicism and smugness of Jason. He has betrayed and wronged Medea but immediately tries to lecture her on her conduct, telling her that if she had meekly submitted to his mistreatment, she could have remained quietly here instead of being banished.

Jason’s arrogance and refusal to acknowledge his guilt certainly lead the audience to think he deserves some kind of punishment. Medea’s revenge on him seems justified insofar as it punishes him but is ultimately unjust and horrifying because it falls also upon the innocent children (as well as his bride to be) and, of course, even on Medea herself as a mother.

The sympathy Medea has built up over the course of the play makes the murders she commits even more shocking to the audience.

In order for the audience to sympathize with Medea, there first has to be a basis for that sympathy within Medea herself. In other words, the audience must be shown, or otherwise assume that, deep down, Medea is essentially a good and noble person.

At the beginning of Euripides's Medea, the Nurse provides the audience with the background of the play. Medea and Jason have fled to Corinth with their two sons after Medea took revenge on King Pelias, who tasked Jason with obtaining the Golden Fleece. Medea caused Pelias to be murdered by his own daughters. She also murdered her own brother, Apsyrtus, in order to aid in their escape to Corinth.

Jason has since forsaken Medea and married Glauce, the daughter of the local king, Creon. Medea is overcome with grief and rage, and vows revenge against Jason.

The Nurse, who loves Medea, nevertheless knows all too well that Medea will wreak a terrible vengeance on Jason. The Nurse also fears that Medea and Jason's young sons will play a part in Medea's revenge against Jason.

An Attendant appears with the children and tells the Nurse that Creon intends to banish Medea for vowing revenge against Jason. This causes the Nurse to be even more concerned for the safety of the two boys.

The Nurse confides her fears to the Attendant.

NURSE. Go: run into the house, my little ones:
All will end happily! ... Keep them apart:
Let not their mother meet them while her heart
Is darkened. Yester night I saw a flame
Stand in her eye, as though she hated them,
And would I know not what. For sure her wrath
Will never turn nor slumber, till she hath ...

At this point, Medea's voice is heard from inside her home calling out in grief and pain, and the Nurse and the Attendant break off their conversation.

In time, Medea affects her revenge. She kills her children, Creon, and Creon's daughter, Glauce, leaving Jason alive to suffer the rest of his life in loneliness and grief.

Although Medea suffers from excessive selfishness and pride (hubris)—flaws shared by many of the tragic characters in ancient Greek tragedies—her greatest and most tragic flaw (her hamartia) is an excess of passion. Medea is driven to her murderous behavior by her excessive jealousy, hatred, rage, and overwhelming need to take revenge on anyone who wrongs her.

It's true that Medea is wronged by Jason and Creon, and she's suffered terrible misfortune in her life, but is Medea a person for whom the audience can feel sympathy? Is Medea any less to blame for her circumstances than Pelias, Creon, or Jason?

While many audience members can feel pity for Medea and experience fear at her self-destruction—which Euripides no doubt intended them to feel—few members of the audience can truly sympathize with Medea or emphasize with her by putting themselves in Medea's situation. They simply wouldn't kill their own children, no matter the motivation or provocation.

I'm not entirely sure that Euripides does intend us to sympathize with Medea; at least not completely, at any rate. After all, she does murder her own children, and infanticide was no more morally acceptable then than it is today. But all this happens later on in the play. Long before Medea takes a dark turn and slaughters her kids, Euripides gives us plenty of reasons to feel at least a twinge of sympathy for her.

First and foremost, she is a wronged woman. She defied her father and took enormous personal risks to help Jason escape. Yet he repaid her courage, love, and kindness by dumping her for another woman. Medea gave up everything to be with Jason, but his cruel abandonment of her has left her an outsider in Corinth, a foreigner without a home or a family. Without a support network, Medea is effectively a non-person, completely vulnerable and without protection. Under the circumstances, it's no wonder that she wants to exact such a terrible revenge upon the man who betrayed her.