Perseus is the son of Danae, a mortal woman who was impregnated when Jupiter rained down on her in a shower of gold.
We first meet Perseus when he is zipping over the earth in a pair of winged sandals.
One evening, Perseus comes to the garden of the Titan Atlas – who lives further west than anybody else. Atlas's garden contains the famous "Apples of the Hesperides" – golden apples growing on a golden tree with golden leaves.
Because Atlas had heard a prophecy that his apples would be stolen by a son of Jupiter, he refused to let Perseus come in. In response, Perseus reached into his rucksack and pulled out…the head of Medusa, which turns whoever looks at it to stone. (Perseus had earlier killed and decapitated Medusa.)
When Atlas sees Medusa's head, he instantly turns into a giant mountain. That mountain, Ovid tells us, now supports the heavens. Then Perseus leaves.
As Perseus is flapping his way along, he comes to the land of the Ethiopians. On the beach, he sees that the Ethiopian princess, Andromeda, has been chained to a rock by her father, King Cepheus, to placate the god Ammon.
(The back-story is that Andromeda's mother, Cassiope, had boasted that she was more beautiful than the Nereids, a.k.a. sea-nymphs. When Cepheus, the Ethiopian king, asked the oracle of Ammon what he should do, the oracle said to chain his daughter to a rock by the sea.)
Perseus quickly flies down to help Andromeda. At first, he tries to engage her in chit-chat, without much success. Then, all of a sudden, a huge monster arises out of the deep. It is coming to eat Andromeda!
Now Perseus sees his chance. He calls out to Andromeda's parents, the King and Queen, and says that, if he kills the monster, they have to accept him as their son-in-law. They agree to his terms.
As you might expect, Perseus battles the monster and kills it.
During the celebrations that follow, Perseus puts the head of Medusa on the sand. So that it isn't damaged, he makes a bed of plants underneath it; then he puts the head face-down on top of it. As it turns out, the plants soak up the power of Medusa's eyes, and turn to stone. When Perseus throws them into the sea, they become the first coral.
Then Perseus makes sacrifices in honor of the major gods, and claims Andromeda as his wife. At the wedding feast, someone asks him to tell how he killed Medusa.
Perseus clears his throat and starts telling about his adventures. Here's what he says:
First, Perseus stole the eye of the Graeae – three weird witch-like women who only had a single eye that they passed between them like a hot potato. Just when it was changing hands, Perseus reached in and stole it.
Then he went to find Medusa and kill her. He had figured out a way to look at her without turning to stone: by looking at her reflection in his shield. With this stratagem, Perseus successfully killed and decapitated Medusa.
Where Medusa's blood landed on the ground, two creatures sprang up: Chrysaor and Pegasus. Ovid doesn't tell us anything about Chrysaor, though according to tradition he was either a giant or a winged boar. Pegasus was a winged horse.
That's the end of the first part of Perseus's story. Then he goes on to tell about his other crazy adventures. At some point, one of the guests at the banquet interrupts him, wanting to know why Medusa had snakes for hair.
Perseus says that Medusa used to be a very beautiful woman. Her most beautiful feature was her hair. In fact, her hair was so beautiful that it made Neptune, the god of the sea, inflamed with lust – to such an extent that he raped her in the temple of Minerva. Minerva didn't like this one bit, and decided to punish Medusa. Thus, she turned Medusa's hair into serpents.
Perseus and Andromeda's wedding banquet does not go as planned. In the midst of the festivities, the king's brother, Phineus, starts making an uproar.
He claims that Perseus has stolen his rightful bride, Andromeda (who is also his niece). Even though King Cepheus tries to talk him down, Phineus throws a spear at Perseus, but misses him.
Then all hell breaks loose, as the banquet erupts into a battle. Perseus kills various men.
Eventually, Perseus ends up without a weapon, facing hordes of incoming enemies. He decides it's time to bust out the big guns – and lifts up the head of Medusa.
Now, everyone who tries to attack him turns to stone. Perseus also accidentally turns to stone somebody on his own side – his friend Aconteus.
Finally, when almost all of his friends have been turned to stone, Phineus throws himself at the mercy of Perseus, begging for his life. He averts his eyes, so as not to look at Medusa.
In response, Perseus says, "Don't worry; I want to keep you around my palace forever." Then he puts the Medusa head in front of Phineus's eyes and turns him into a statue.
Next Perseus continues to wander the world. In his travels, he uses the Medusa head to turn various annoying people to stone.