King Acrisius of Argos had only one child, a daughter, named Danaë. She was beautiful above all the other women of the land, but the King was not content because he had yet to have a son. Journeying to Delphi, he was told by the priestess that he would never be the father of a boy, and even worse, his daughter would have a son who would kill him.
To escape his fate, he ensured that Danaë would not have any children. He shut and guarded her in a house built of bronze and sunk underground. He hoped that in this way, he would not have to kill her and spare his own life. One day, Zeus visited her and she bore his son. For a time, she tried to conceal the child from her father, but the narrow limits of the bronze house made it increasingly difficult and soon Perseus was discovered by his grandfather. Acrisius was very angry but was afraid to kill the boy or his mother because he feared Zeus. He had a great chest made, placed the two in it, and brought it to the sea and cast it into the water. The chest was tossed out to sea and finally one-day, they landed on an island but they had no way to get off it.
Fate willed it, or even Zeus, that they were be discovered by a good fisherman, name Dictys. He came upon the box, broke it open and took them home to his wife who was as kind as he. The two lived there for many years, Danaë was content to let her son follow the fisherman's humble trade. But in the end more trouble came, Polydectes, the ruler of the small island (and Dictys' brother) fell in love with her. He wanted her, but not her son (who was now fully grown), and he set himself to think of a way of getting rid of him.
There were some fearsome monsters called Gorgons who lived on an island and were known far and wide because of their deadly power. Polydectes probably talked to Perseus and told him that there was nothing that he rather have than a head of one of them. He announced that he was to be married and called his friends to the celebration, including Perseus. Each guest, as a custom, brought the bride-to-be a gift, except Perseus alone. Mortified, he stood up and declared that he would go off and kill Medusa (which was one of the Gorgons) and bring back her head as his gift. This was exactly what the king had planned. There were three of them and whoever looked at them was turned instantly to stone.
Not daring to see his mother, he sailed off to Greece to learn where the monsters were to be found. He went to Delphi, but all the priestess could tell him was that the men should not eat Demeter's golden grain but only acorn. He then traveled to Dodona where the Selli lived and made their bread from acorns. They did not know where the Gorgons lived.
When and how Hermes and Athena came to his help was not known but he must have known despair before they did so. At last, however, as he wandered, he met a strange and beautiful person none other than Hermes, the guide for the giver of good. This radiant person told him that before he attacked Medusa, he must first be properly equipped, and that what he needed was in the possession of the nymphs of the North. To find the nymph's abode, they must go to the Grey Women land where all was dim and shrouded in twilight. The three other women were all grey themselves and withered as in extreme age. They had but one eye for the three, which they would take turns with, each removing it from her forehead after she had had it for a time and then handing it to another. Hermes unfolded the plan. He would lead Perseus to them and when they arrived, he would remain hidden until one of them took their eye out of their forehead to pass it on. At that moment, he would rush forward and seize the eye and refuse to give it back until they told him how to reach the nymphs of the North. Hermes gave Perseus a sword to attack Medusa, which could not be bent or broken by the Gorgon's scales. This was a wonderful gift, but what use was a sword if the creature to be struck by it could turn it into stone before he was within striking distance? Pallas Athena stood beside Perseus and she took off the shield of polished bronze and gave it to him. She told him he would be able to see Medusa in it as in a mirror, and so avoid her deadly power.
When they found the Grey Women, Perseus carried the plan and was successful in learning where the nymphs of the North lived. And so without knowing, he was bound for the country of the Hyperboreans. No one had been able to reach the place of the Hyperboreans but since Hermes was with him, the road laid open to Perseus. There he found a host full of people always banqueting and holding joyful revelry, who welcomed him kindly. They gave him three things: winged sandals, a cap which made the wearer invisible, and a magic wallet which would always become right size for whatever was to be carried in it.
Now, Perseus was ready for the Gorgons and Hermes knew where they lived. So the two flew back across the ocean and over the sea to the Terrible Sisters' island. Luckily they were asleep when Perseus found them. In the mirror of the shield, he saw the creature with great wings and bodies covered with golden scales and hair a mass of twisting snakes. Athena and Hermes pointed out which one was Medusa because the other two were immortal. With a single sweep of the sword, he cut her neck and his eyes were fixed on the shield with never a glance at her, he swooped low enough to seize her head. He dropped it into the wallet, which closed around it. The other two Gorgons woke up horrified at the sight of their slain sister, they tried to pursue the slayer, but Perseus had on the cap of darkness and they could not see him.
On his way back, he came to Ethiopia and found that a lovely woman was about to be devoured by a horrible sea serpent. Her name was Andromeda. When Perseus arrived, the maiden was on a rocky ledge by the sea, chained there to wait for the coming of the monster. Perseus found her and on the instant loved her. He waited beside her and when the great snake came for its prey, he cut off its head. Perseus took Andromeda to her parents and asked for her hand, which she gladly gave him.
When he returned to the island, where he lived for so long, he found no one. The fisherman's wife had died long ago and Dictys and Danaë had fled from the furious Polydectes when she refused to marry him. They had taken refuge in the temple. The king was having a banquet at the palace, and Perseus seized the opportunity. He walked into the palace and took out the head of Medusa and all the guests and the King were turned into stone. When the islanders knew that they had been freed from the tyrant, Perseus found Danaë and Dictys. He made Dictys king of the island and he and his mother returned with Andromeda to Greece to reconcile with Acrisius. When they reached Argos, they discovered that Acrisius had been driven away. Perseus heard that the King of Larissa was holding a great athletic banquet and he journeyed to take part. In the discus-throwing competition when his turn came and he hurled the heavy missile, it swerved and fell among the spectators. Acrisius was there on visit and the discus struck him and he died at once.
Through this act, Apollo's oracle proved to be true. Perseus and Andromeda lived happily ever after. Their son was Electryon, who was the grandfather of Hercules. Medusa's head was given to Athena, who bore it always upon aegis, Zeus' shield, which she carried for him.