None too happy, but unwilling to provoke the wrath of the gods by killing his offspring, Acrisius cast the two into the sea in a wooden chest. They washed ashore on the island of Seriphos, where they were taken in by Dictys, the brother of king Polydectes, who raised the boy to manhood. Now after a time Polydectes fell in love with Danae, and so wanted to get Perseus out of the picture. He thereby hatched a plot to send him on a suicide mission.
Polydectes placed some strong hints that he would love to have the head of Medusa, one of the gorgons whose very expression turns people to stone. He then announced that he would woo Hippodamia and so needed the others to provide him with horses (a different myth). Shamed at having nothing to give, Perseus left to get him Medusa's head. This was of course not easy, and for a long time he wandered aimlessly, without hope of ever finding her or being able to accomplish his mission when he did.
The gods Hermes and Athena came to his rescue. They led him to the Graeae, three perpetually old women with one eye and tooth between them and sisters of the gorgons. Perseus took the eye and would not return it until they had given him directions. He also received winged sandals, a magic wallet, the cap of Hades that made one invisible, an adamantine sickle, and a mirrored shield. With all this he came upon the sleeping gorgons. By viewing Medusa's reflection in his shield he could safely approach and cut off her head. The other two gorgons pursued him, but he became invisible and escaped.
On the way back to Argos, Perseus stopped in Ethiopia, ruled by King Cepheus and Queen Cassiopeia. Cassiopeia, having boasted herself equal in beauty to the Nereids, drew down the vengeance of Poseidon, who sent an inundation on the land and a sea-monster which destroyed man and beast. The oracle of Ammon having announced that no relief would be found until the king exposed his daughter Andromeda to the monster, she was fastened to a rock on the shore. Here Perseus, returning from having slain the gorgon, found her, slew the monster, set her free, and married her in spite of Phineus, to whom she had before been promised. At the wedding a quarrel took place between the rivals, and Phineus was turned to stone by the sight of the Gorgon's head (Ovid, Metam. v. 1). Andromeda followed her husband to Tiryns in Argos, and became the ancestress of the family of the Perseidae through Perseus' and Andromeda's son, Perses. After her death she was placed by Athena amongst the constellations in the northern sky, near Perseus and Cassiopeia. Sophocles and Euripides (and in more modern times Corneille) made the story the subject of tragedies, and its incidents were represented in numerous ancient works of art.
And on returning to Argos and discovering his mother had had to take refuge from the violent ways of Polydectes, he killed him, and made Dictys king.
Perseus then returned his tools and gave Medusa's head as a gift to Athena. He started for Argos, but learning of the oracle instead went to Larissa, where athletic games were being held. By chance Acrisius was there, and Perseus accidentally struck him with his javelin, fulfilling the oracle. Too shamed to return to Argos he then gave the kingdom to Megapenthes son of Proetus (Acrisius' brother) and took over his kingdom of Tyrins, also founding Mycenae and Midea there.
Abas was a good friend of Perseus.
Perseus and Andromeda had six sons: Perses, Alcaeus, Heleus, Mestor, Sthenelus, and Electryon. The first was supposedly left in Ethiopia and became ancestor of the emperors of Persia to explain the similarity of the country's name and Perseus'. His descendants ruled Mycenae from Electryon down to Eurystheus, after whom Atreus got the kingdom, and include the great hero Heracles son of Amphitryon son of Alcaeus.