This story begins with Perseus' grandfather, Acrisius, who was the king of Argos in central Greece.  Acrisius had received an oracle indicating that he would someday be killed by his grandson. Since he had only one daughter, the beautiful Danae, Acrisius thought he could prevent his fate by preventing her from ever marrying and having children.  He built a special bronze room, open to the sky but with no windows or doors, and locked her in before puberty.  He supplied her with food and clothing but no companionship and definitely no contact with men.  The bronze enclosure could not keep out the god Zeus, however, and since Danae was very beautiful and since her room was open to the sky, it was not long before Zeus attempted to seduce her.  He visited Danae in his most abstract and unusual form, as a shower of golden raindrops, and soon Danae was pregnant.

    When Danae gave birth to her son Perseus, Acrisius discovered his betrayal.  He put Danae and Perseus in a chest with a few holes poked in it and floated it out to sea where he was certain they would drown.  But Zeus, of course, watched over them until they floated ashore on a nearby island.  Here they were taken in by a friendly fisherman (Dictys) who was the brother of the evil king of the island, Polydectes.  Polydectes quickly learned of Danae's beauty and wanted to marry her but she managed to put him off until Perseus was a young man.

    As soon as Perseus was old enough, he went to Polydectes' palace and demanded that he quit bothering Danae.  Polydectes was surprisingly cooperative but he persuaded Perseus that he should provide Polydectes with some compensation for the loss of Danae, a valuable gift like the head of the Gorgon, Medusa, for instance.  This was the pretext or excuse for Perseus to go after this famous monster.  Like Jason's uncle Pelias, Polydectes was sure that Perseus would never return.

    The Gorgons were three sisters who had once been beautiful.  But their pride in their good looks had offended Athena and she had turned them into monsters with snakes growing out of their heads, scaly bodies, and boar's tusks.  Of the three, only Medusa was immortal, and her stare was so potent that anyone who looked at her turned to stone.  The  Gorgons lived on an island somewhere in the far western Mediterranean.

    Perseus' first task is to find out where the island is.  (This was also a problem for Heracles and the apples of the Hesperides).  Perseus must consult the gray ladies (Graeae) who have one eye and one tooth to share between them.  Perseus grabs the eye and the tooth and holds them for ransom until the Graeae reveal the location of Medusa's island.  They also send Perseus to the Stygian nymphs who give him three invaluable gifts:  winged sandals (he must fly to the island; there are no boats as yet), a helmet of invisibility, and a bag to put the head in eventually.  Other useful devices that Perseus will need include:  a sharp knife which he gets from Hermes, and a shield polished like a mirror that he gets from Athena.

    With the help of the winged sandals, helmet of invisibility, polished shield, and curved knife, Perseus is able to sneak up on and slay the Medusa without havng to look directly at her  and puts her head in his bag.  From the stump of Medusa's body springs Pegasus, the winged horse, whose father was Poseidon.

    On his way back to Polydectes, Perseus has a side adventure.  He is able to rescue the beautiful princess Andromeda whose father is about to sacrifice her to an angry sea monster.  (Look up Andromeda for the rest of this story).  Perseus uses the Medusa's head to freeze and destroy the sea monster and then takes Andromeda home with him to marry.  When they return to Polydectes' palace, Perseus whips out the Medusa's head again and turns the king and all his courtiers to stone.  Now his mother is free of harassment and Perseus departs for the mainland to claim the throne of Argos.

    Before he gets there, he stops for athletic competition at Larissa.  There he tries to throw a discuss which spins out of control and into the crowd of spectators.  Who should be among the spectators but Perseus' grandfather Acrisius himself.  He is hit by the metal discuss and he dies.  So the oracle is fulfilled and he didn't escape it after all.

    The Medusa's head is presented to Athena and she puts it on her breastplate (aegis) where it will be part of her formidable defenses.