With Medusa's head tucked into his kibisis (supernatural backpack), Perseus soars above Ethiopia with his trusty winged sandals. (To find out where he got the head of Medusa, and why he's flying over Africa, click here.)
When he gets to the ocean, he notices a girl chained to a rock in the crashing waves.
Perseus instantly falls in love with the beautiful maiden, as is always the case in these kinds of stories.
He streaks down from the sky to find out why such a pretty girl is chained to such a big nasty rock.
Our hero learns that the girl's name is Andromeda. She's the daughter of Cepheus, who is the king of Ethiopia.
It turns out that Cepheus has chained Andromeda to the rock to feed Cetus a giant, maiden-eating sea monster. Why? Good question. Here's the story:
Not long ago, Andromeda's mother, Cassiopeia, bragged that her daughter was far more beautiful the Nereids, minor goddesses of the sea. [In some versions of the story, Cassiopeia said that she herself is more beautiful than the Nereids.] This claim seriously ticked off the Nereids, so they complained to Poseidon, the great god of the sea.
Poseidon decided to punish all of Ethiopia for Cassiopeia's boast. He swore to send a giant flood and the Cetus, a sea monster, to destroy the land. The only thing that will make Poseidon chill out is if Andromeda is offered up as a sacrifice to the hungry sea monster.
When Perseus learns all this, he flies off to the king and says he'll slay the monster in return for Andromeda's hand in marriage. King Cepheus is like, "Sure, go for it."
An epic battle ensues, and Perseus kills the monster.
In some versions, Perseus uses Medusa's head to turn the Cetus into stone, while in others he just uses a sword.
Some versions also say that Perseus sets Medusa's head down while battling the monster, and that, when the Gorgon's blood drips into the water, it petrifies the seaweed, making the first coral reefs.
After defeating the monster, Perseus and Andromeda head back to the palace, get hitched, and everybody has a big party.
It turns out, though, that Andromeda was already engaged to her uncle Phineus.
Phineus gets pretty mad that his fiancée got married to somebody else and challenges Perseus.
To shut up the angry Phineus, Perseus whips out the head of Medusa and turns Andromeda's uncle to stone.
After that, Perseus and Andromeda fly away for Seriphus, Perseus' island home.