King Acrisius was worried about not having sons so he visited the oracle and she said that he would never have sons. Only a daughter that will one day have a son that will kill him and become king
to make sure he didn't have a grandson he locked his only daughter, Danae in a cell and said he would never let her out. she prayed to the gods and Zeus heard her. He came down as a golden rain to visit her and 9 months later she had Perseus.
king Acrisius was furious that he now had a grandson, so he ordered his solders to throw is daughter and grandson into the ocean. Danae prayed to the gods again, and Zeus gave her rain to drink, Poseidon calmed the sea and guided it towards land and sent little fish for her to eat.
Danae was rescued by a fisherman named Dictys and he took Danae and baby Perseus to the king Polydectes. Polydectes wanted to marry Danae so he could become the ruler of both cities, Seriphos and Argos.
17 years passed, as Perseus grew up on the island. The king still hasn't convinced Danae to marry him, because Perseus keeps getting in the way. So, the king comes up with a clever plan, he gets him to promise to give the gift of anything he wants, and the king asked for Medusa's head.
Perseus prayed for the gods to help him on his quest, so Zeus sent Hermes. Hermes gave Perseus a sac, a helmet that makes him invisible, and sandals with wings, so he could fly. Hermes then sends Perseus to go find the gray sisters.
Perseus finds the gray sisters, steals their eye, and makes them tell him how to find medusa in order to give the eye back.
Perseus digs up the sword and shield and Athena shows up while he is digging and gives him hints on how to find and kill Medusa.
He found medusa in a cave with a lot of stone people that tried to kill medusa, but were turned into stone in the progress. He then successfully killed medusa and stuffed her head in his sac. Two creatures also came out, Pegasus and Chrysaor.
Perseus was lost, he went too far south and wanted to ask someone for directions. He then saw a beautiful girl chained to a rock, which was being sacrificed to please Poseidon. Perseus then slayed the monster by pulling out medusa's head in his sac.
Perseus brings medusa's head back to king Polydectes but he did not know that he was in for an ambush. Perseus then said "everybody who is with me close your eyes", and that was the end of the solders.
Perseus took his wife Andromeda back to Argos. On the way, he returns the gifts to the gods and gives Medusa's head to Athena to put on her shield. King Acrisius heard that he was coming, so he ran away and Perseus took the throne and became king.And what about the prophecy? well, years later Perseus went to the Olympic type games and was throwing the diskus, when he accidentally hit and killed an old man, who turned out to be his grandfather, king Acrisius.