Although the play is confined in time to the final day of catastrophe at Corinth, the background is the whole romantic story of the Argonauts: how Jason and his hero-comrades, at the instigation of Pelias, the usurping king of Thessalian Iolchos, undertook the first voyage in quest of the golden fleece; how, after many adventures, these first sailors reached the kingdom of Aeëtes who jealously guarded the fleece, since upon its possession depended his own kingship; how the three deadly labors were imposed upon Jason before the fleece could be won—the yoking of the fiery bulls, the contest with the giants that sprang from the sown serpent's teeth, and the overcoming of the sleepless dragon that ever guarded the fleece; how, smitten by love of him, the beautiful, barbaric Medea, daughter of the king, by the help of her magic aided Jason in all these labors and accompanied him in his flight; how, to retard her father's pursuit she slew her brother and scattered his mangled remains in the path as they fled; how again, for love of Jason, she restored his father to youth and tricked Pelias' own daughters into slaying their aged sire; how, for this act, Medea with her husband were exiled from Thessalia and dwelt in Corinth; how, for ten happy years, she lived with her husband and two sons in this alien land, her wild past almost forgotten, her magic untouched.
But now, Jason has been gradually won away from his wife, and is about to wed Creüsa, the daughter of Creon, king of Corinth. The wedding festivities have, already begun when the play opens and reveals Medea invoking all the powers of heaven and hell in punishment of her false lord.
