A Greek king, Athamas, gets tired of his wife Nephele and puts her jail. He marries Io, a young princess, in her place. Nephele prays that Io will not kill her two children in order to make Io’s own children inherit the kingdom. Io does attempt this murder, however. She secretly gathers seed-corn and parches the seed so that no crops will grow. Then, when Athamas asks for word from an oracle about how to end the famine, Io bribes a messenger to say that the only way to bring back the crops is to sacrifice his son, Phrixus. Athamus and Io bring the boy to the sacrificial altar, but just before the murder, a wondrous ram with a golden fleece takes the boy and his sister and runs away. The ram, sent by Hermes, is an answer to Nephele’s prayers.
The ram carries the children across the water from Europe to Asia, and on the way, the girl slips off and drowns. Phrixus arrives safely in the country of Colchis, where he sacrifices the ram and gives it to King Etes.
Meanwhile, in another part of Greece, a king named Pelias has stolen the crown from his brother. An oracle tells him that he will die at the hands of a kinsman and that he should be wary of a man wearing only one sandal. One day, a man wearing one sandal comes to town. This is Jason, the king's nephew, come to claim his rightful place as king. Pelias tells Jason that he would give up the throne if Jason would go out and retrieve the golden fleece. Jason sets off and overcomes many obstacles and adventures on the way to Colchis. Finally, with the help of Hera, he reaches King Etes.
Hera and Aphrodite arrange for Cupid to make King Etes's daughter, Medea, fall in love with Jason. Jason asks Etes for the fleece, but Etes says Jason must plow a field of dragon's teeth, which will spring up into a crop of armed men who must be cut down as they advance and attack. Jason agrees, though he believes the task will result in his death. Thanks to Cupid's bow, however, Medea gives Jason a magical potion that gives give him invincibility for one day. She also tells him to throw a rock into the middle of the army because it will lead the armed men to kill each other. The next day, Jason proves victorious.
The treacherous king will not give him the fleece, however. He plans to kill Jason. Medea helps him again. She leads him to the fleece, charms the serpent guarding it, and flees with Jason back home.
On the journey home, Medea kills her brother in the idea that she is protecting Jason. This is the first sign of her madness. When they return to Greece, she arranges for King Pelias to be killed by his own daughters, which fulfills the oracle. Later, Jason marries another woman, and Medea becomes so angry that she kills both the bride and her own two sons fathered by Jason.
The story of the Quest for the Golden Fleece highlights the dangers of selfishness and jealousy. King Athamas, King Pelias, and Media all drive the people around them (and themselves) into chaos as a result of their self-serving motives. The story also reveals complex family loyalties. Various family members are jealous of outsiders and other insiders, and they are willing to kill to achieve their goals. Medea arranges for Pelias to be killed by his own daughters. Later, she kills her own children and Jason's new bride to exact revenge. Io attempts to kill Nephele's children.
In other instances, characters go out of their way to save people in their families. Medea kills her own brothers to protect Jason, wisely or not. Nephele prays to Hermes to save her children. In all of these situations, family loyalties are as strong as they are complex. Only Jason and Nephele appear to have purely ethical intentions and clear loyalties.
The human sacrifice is interrupted by the ram with the golden fleece (compare the story of Abraham and Isaac in Genesis and some versions of the Greek myth of Iphigenia). Instead of taking the place of the ones to be sacrificed, this ram escapes along with them. The fleece of the ram seems to hold special redemptive power. It becomes an almost magical item worthy of a quest. In order to retrieve it, Jason needs the help of Medea as well as some magic and divine help.
Medea first proves selfless in helping Jason win the golden fleece, but she eventually crosses a mental boundary and acts unforgivably. This mad selfishness, made worse by jealousy, reveals some psychological depth in her character. Throughout Western literature and theater, she stands as an unforgettable example of the duality in human nature, the combination of the rational and the irrational, as well as an example of the horrifying consequences of jealousy.
As in other stories, the gods involve themselves in human affairs to effect the outcome they perceive as positive. As with Bellerophon and Theseus, they support Jason, the hero, in his noble quest to defend his family and his position as king. The gods also answer Nephele's prayers, which underscores the recurring theme that the gods sometimes listen to humans.