We first meet Medea when Jason arrives in her father's kingdom, looking for the Golden Fleece.
Medea's father, King Aeëtes, tells Jason, "OK, I'll give you the Golden Fleece, but first you have to perform three tasks for me…" (Insert ominous music here.)
Ovid doesn't tell us what these tasks are, however; not right away, at least. Instead, he lets us know that Medea, King Aeëtes's daughter, has developed a major crush on Jason.
At this point, Medea delivers a long dramatic monologue, in which she reveals her feelings for him. She is particularly worried about the dangers Jason is about to face – the three tasks set by King Aeëtes, which we now learn are: (1) to put a yoke on a pair of fire-breathing oxen; (2) to sow (i.e., plant in a furrow) the teeth of the snake slain by Cadmus; and (3) to overcome the dragon that guards the Golden Fleece.
Medea's thoughts wander to and fro, as she considers helping Jason and running off with him. Eventually, however, she decides against it.
Then, however, she sets out for the shrine of the goddess Hecate. On the way, she encounters Jason, and instantly is overpowered by love. When she approaches him, he begs for her help in the coming tasks. She promises to give it, provided that he will marry her. He promises he will.
The next day, King Aeëtes and his people go out to the field to see Jason confront his challenges. First, Jason yokes the fire-breathing bulls – piece of cake. Then, he ploughs the field and throws the snake's teeth in the furrows. In no time, the snake's teeth germinate into a race of warriors, who spring up out of the earth fully armed – and ready to attack Jason.
Watching all this, Medea is afraid for Jason, and she casts a spell to help him. We aren't told what the spell is, but if might have something to do with what happens next: Jason throws a stone into the middle of the undead warriors. This distracts them, and they start fighting each other. They fight until they are all dead – again.
Last in the list of challenges is the dragon. Jason walks up to it and sprinkles some herb juices on it. We don't know what kind of, uh, herb, this was, but it sure makes the dragon fall asleep – thus giving Jason a window of opportunity to snag the Golden Fleece. He then sails away with his new treasure – plus Medea, his new girlfriend (but she thinks they're more serious than that).
When Jason and his crew get back home, everyone celebrates – except for Aeson, Jason's elderly father, who is at death's door. Saddened by this, Jason asks Medea if she can just, you know, take some of his years and give them to his father. Medea says no way is she going to take years from Jason – but she might just try to whip up some magic to make Aeson live longer.
That night, Medea goes out into the woods and prays to the various divinities of the earth and sky. She asks them for some juice that will prolong old Aeson's life.
When she is done praying, a chariot swoops down from the sky to pick her up. Medea's got connections, you see: her granddad is the Sun.
She gets into the chariot, which is pulled by two dragons. In it, she travels the world for nine days and nine nights. At the end of this period, she finds the herb she's looking for. Then she heads back to the palace of Aeson.
There, she performs some wacky purification rituals on Aeson. Then, she brews up a potion using the herb she had plucked. She knows it's ready when the olive stick she stirs it with turns green and sprouts new leaves; then when she carries it over to Aeson, wherever droplets fall on the ground, grass springs up.
What does she do then? Why, she pulls out a sword and cuts Aeson's throat.
But that's just to drain his old blood out. Then she fills him up with the potion, and he revives – forty years younger!
After this, Medea heads to the palace of King Pelias – Aeson's brother and Jason's uncle. Jason has been having some problems with his uncle, and now Medea wants to settle King Pelias's hash.
When she arrives at his palace, the first people she approaches are Pelias's daughters. She boasts to them of how she revived Aeson; this makes the girls excited that she can do the same for their own father.
At first, Medea plays hard to get, saying, "Hmmm, I don't know. Let's make sure it still works first. Here: let me turn that old ram over there into a lamb." And that's exactly what she does, complete with the throat cutting, blood draining, and all.
The daughters of Pelias are so impressed by this that they insist Medea do the same for her father. She agrees, and three days later they start the ritual. This time, Medea gets the daughters to stab their father and drain his blood themselves.
Even though Pelias's daughters can't bear to watch what they're doing, they stab him anyway. Of course, this time Medea uses a placebo potion without any magic herbs. Guess what? Pelias dies.
Then Medea hops into her dragon chariot and says, "Let's blow this popstand." And she's off!
Medea flies all over the world, passing various landmarks where weird transformations occurred. Finally, she comes back to Corinth – where she discovers that Jason has married someone else!
What's a wronged woman to do? Well, if you're a wronged woman and your name happens to be Medea, you start by killing your lover's new wife by setting her on fire; then you kill your children with the creep (apparently Jason and Medea had children); then you fly away again in your dragon-pulled sun chariot. Are you getting all this down?
Medea takes refuge in Athens, where she marries the local king, Aegeus.
One day, Aegeus's long lost son, Theseus, shows up at the palace. For no apparent reason, Medea decides to kill Theseus.
She conspires with Aegeus to spike Theseus's drink with some slobber taken from Cerberus, the three-headed dog of the underworld. Yikes. But then, just as Theseus is about to put the drink to his lips, Aegeus recognizes the symbol embossed on the young man's sword-hilt, and realizes that he is about to poison his son. He smacks the drink out of the Theseus's hand.
At this point, Medea decides it's time to make herself scarce – so she disappears into a mist of invisibility. How convenient. That's the last we hear of her.