Human affairs, the Messenger philosophizes, are only shadows. No mortal is happy. One can only be more or less fortunate, not happy. His long, expository monologue concludes and the Chorus says that Jason earned this great calamity. It pities the Princess for her attachment to Jason.
By pitying her, the Chorus seems to acknowledge the lesser guilt of the Princess compared to Jason and Creon. Fair judgment and punishment, after all, was not then nor now thought of as tragic. It was the Princess's poor luck and fate that were the source of her doom.
Medea tells the Chorus she is resolved to kill the children and leave Corinth. She says she won't leave them for another to kill, that they have to die, and so, since she gave them birth, she would rather kill them herself. She questions herself for hesitating and tells her hand to take the sword. She tells herself to forget her children for this one day and then mourn. She exits with the children through the door.
Medea introduces the only somewhat plausible argument that, if she doesn't kill her child, her enemies will. Couldn't Medea channel her resources into protecting her children? Nonetheless she is resolved and takes the children offstage. It is significant that none of the deaths in Medea take place onstage. They are all concealed.
The Chorus begins its fifth choral ode. It asks Earth and Sun (Helios) to look down at what Medea is doing. She is Helios' granddaughter, so he should take special interest. It begs Helios to stop her. Have all Medea's travails been for nothing? It calls it terrible for a mortal to shed a family member's blood. The gods punish it. The children are heard screaming offstage. One of the children asks (from offstage) what he can do to escape. The other says he doesn't know.
The Chorus suggests that the death of Medea's children will mean that Medea has lived a pointless life and points out the severity of the breech of Natural Law encompassed in child-murder. It notes that the gods punish such crimes but fails to note that Medea herself is, in part, divine. The children speak for the first time, if only to make them seem more innocent and their being murdered more tragic and awful.
The Chorus asks if it should enter the house. The children cry for help. The Chorus calls Medea miserable and made of stone for killing her children. Only one woman that they know of, Ino, killed her own sons when she was driven mad by the gods. She killed herself and her children by jumping with them into the sea.
The Chorus compares the story of Medea to another story of child-murder in Greek mythology—that of Ino. One significant difference in the two myths is that Ino, crazed by the gods, also killed herself with her children. Medea, according to the Chorus, is entirely unique for deciding to kill her children and go on living.
Jason enters and questions the Chorus if Medea is still in the house. He says she will either have to hide beneath the earth or fly into heaven if she is to escape punishment. He cares about the children, however, and is worried his new relatives might do something to them to avenge Creon and the Princess's murder. The Chorus pities Jason's ignorance. He thinks that the Chorus means she intends to kill him. They let him know that his children are dead.
Jason accidentally, ignorantly predicts Medea's mode of escape (into the heavens). Jason's anxieties about the boys' safety at the hands of Creon's angry relatives underscores how much their deaths will hurt him. The Chorus pities Jason for always knowing less than it, Medea, and the rest of us. For not knowing what we and they know, he is constantly the victim of dramatic irony.
Jason asks where the children were killed. The Chorus tells him to open the door. He commands his servants to undo the bolts. He wants to see the bodies and take vengeance on Medea. Medea asks why they are rattling and battering the doors. She says if Jason wants her, then he should say what he wishes, but, she adds, he will never lay hands on her again.
Jason at last seeks to break the boundary between interior and exterior represented by the door throughout the play. Yet as a consummate perpetrator of deceit Jason isn't permitted the capacity to reveal the play's interior truth—that Medea has been justly vengeful for his injustice against her.
Medea appears in a flying chariot drawn by chimeras sent by Helios, her grandfather. The notes for the staging don't survive in the manuscript, but the chariot is either on the roof of her house or suspended over the stage by a crane. She has with her the bodies of her dead children.
The gods, especially Helios, appear to condone Medea's actions—they have, after all, sent her a flying chariot to take her to Athens. This machine from the gods (origin of the term "deus ex machina") is a common plot device in ancient tragedy.