Act I
Glauce, daughter of King Creon, prepares for her wedding. She is marrying Jason and is fearful that Medea, his abandoned wife, will seek revenge. Medea has borne Jason two children, and Creon assures him that they will be protected, educated and taught to hate their mother as a wicked sorceress. The Argonauts present Glauce with the Golden Fleece that Jason took from Medea’s father with her help. They toast the couple and invite the god Hymen to attend the wedding.
The Captain of the Guard announces the arrival of a veiled woman who does not want to give her name. Creon grants her entrance, and the woman presents herself as Medea. She asks Jason to come home and warns Creon that he should cancel the wedding. The king answers her threats with threats of his own. Medea reminds Jason of the sacrifices she made for him and begs him to have pity on her as an abandoned mother. When Jason rejects her pleas, Medea swears revenge.
Act II
Medea complains about her lonely fate. Neris, her slave, urges her to escape while she still has time but then they are found by Creon and his guards. The king informs Medea that Jason has asked him to spare her life but that she must leave the country immediately. Medea reminds Creon that without her help in taking the Golden Fleece, Jason would be dead. She asks for asylum so that she could at least see her children occasionally. Creon refuses her request but allows her to stay for one more day.
Neris promises to share whatever fate befalls her mistress but Medea has decided to use her final day for revenge. She asks Jason to let her take the children home with her. He is not willing for that to happen but allows her to be with them until her departure. Medea asks Neris to present Glauce with jewellery and a dress soaked in poison as a wedding present, and she call on Hymen to smile upon her plan.
Act III
Medea tries to calm her pangs of guilt as she prepares to kill her own children. Neris brings them to her and she is overcome with motherly love. The slave informs Medea that Glauce has accepted the wedding gifts and is already wearing the dress. Satisfied that revenge has been served, she asks Neris to take her children to safety.
The wedding guests cry out in horror: Glauce has been killed by the poisoned dress. They rush out in a panic and demand Medea face death for her crime. Jason goes in search of his children but only finds Neris, who tells him that her mistress, who has had a change of mind, plans to kill them. Medea steps out holding a weapon. She tells Jason that she has been avenged by the blood of their children and that he is now free to find himself another wife.