Danae was the daughter of Acrisius. Acrisius learned one day that he will never bear a son, and that Danae's son will kill him. Fearing for his life, he locked Danae in a bronze house underground. Zeus appeared and bore her a son, Perseus.
Acrisius discovered the two and cast them out into the sea in a chest. They eventually ended up on a shore and were rescued by a fisherman named Dictys, who took them into his home. Polydectes, the ruler of the island, fell in love with Danae, but he wanted Perseus gone.
Polydectes devised a plan to kill Perseus: the Gorgons were terrible creatures whose eyes turned anyone who made direct contact with into stone. Polydectes announced that all he wanted was the head of Medusa, and he announced he was having a wedding, and so everyone gave him gifts except Perseus. Mortified, Perseus vowed to give Polydectes the greatest gift he could have: Medusa's head.
In order to accomplish such a seemingly impossible feat, Hermes and Athena aided Perseus. First, Perseus learned from Hermes that he must acquire necessary weapons from the nymphs in the North, and their location can only be known by asking the Gray Ladies. Perseus traveled to the Gray Ladies, where he learned that to get them to speak, he must take their eye (the three sisters each shared an eye) and demand them to give him directions or else he'll keep the eye. As expected, the Gray Ladies gave him directions.
At the nymphs' abode, Perseus received winged sandals, a magic wallet with enough space for anything, and an invisibility cap. Hermes gave Perseus a sword able to pierce any defense, and Athena gave him a shield, which would act as a mirror; Perseus would look at Medusa through this mirror in order to avoid her gaze. Armed and ready, Perseus set out.
In a stroke of luck, Perseus found the Gorgons sleeping. Quickly he beheaded Medusa using his winged sandals and the mirror shield. Medusa's immortal cohorts could not react, as Perseus immediately used his invisibility cap to escape.
On his way back, Perseus spotted a beautiful girl about to be sacrificed to a snake; the girl's name was Andromeda. Andromeda's mother foolishly declared herself to be more beautiful than Nereus's nymphs, a declaration that angered the gods and necessitated a penance act. Instead of punishing the queen, her daughter was chosen instead. Perseus rescued Andromeda, and they planned to marry.
When Perseus arrived back at his home island, he learned that Dictys and Danae had to flee to escape the wrath of Polydectes, who was angry at Danae's refusal of marriage. Perseus heard of a banquet, and everyone was invited to Polydectes's palace. Seeing an opportunity, Perseus seized the chance to enter the palace, attract attention to himself, and hold up Medusa's head. At once, everyone including the king became stone.
Now with the king gone, Danae and Dictys and Perseus reunited, and Perseus made Dictys king of the island. Following this event, Perseus and Danae decided to reconcile with their father Acrisius. When they arrived back home at Greece, they found Acrisius had been driven away; his whereabouts were unknown.
Perseus later heard of an athletic event at the island of Larissa, and he participated. In the discus throwing contest, Perseus accidentally threw the discus which swerved into the crowd, killing Acrisius and fulfilling the prophecy. Relieved at the burden of his father, Perseus and Andromeda lived happily ever after.