Jason (Giasone) has rejected his former wife, Medea, in favour of Creusa, daughter of King Creon (Creonte) of Corinth. Creon banishes Medea from the city and she swears revenge. Meanwhile, King Aegeus (Egeo) of Athens arrives in Corinth. He had been promised Creusa as his bride. Finding he has been rejected, he makes a pact with Medea. As Jason and Creusa are being married in the temple, Medea bursts in with Aegeus's soldiers and a fight breaks out as they attempt to carry off the bride and bridegroom.
Creon's men have defeated and captured Medea and Aegeus. In prison, Medea uses her magic powers to summon up demons from the underworld. She kills Creusa with a poisoned robe then stabs her own - and Jason's - children to death, before making her escape in a chariot pulled by flying dragons. In despair, Jason attempts suicide in vain.