Perseus and his mother were locked in a crate and sent to a small island because of a prophecy that stated that King Acrisius's grandson would kill him. And is taken in by a childless fisherman it was there he would be raised. Because an Oracle had foretold that the grandson of King Acrisius would kill him Perseus being that grandson.
King Polydectes had given Perseus a quest to hopefully get him killed. His task was to slay the monster known as Medusa and bring Polydectes her head. The problem with the task was that no one had ever survived Medusa.
Crossing The Threshold
Perseus was hesitant to accept the quest. And puzzled over the danger. But accepted under the pretenses that Polydectes was going to marry a women other than his mother so he set off to slay the monster and save his mother.
Test Allies and Enemies
Athena first visited Perseus to bestow upon him the shield of brass so he could look at Medusa indirectly in order to slay her. Then Hermes offered up as a guide and to take Perseus to the old women of the gray lands in order to obtain the three magic gifts to aid in his slaying.
Perseus goes with Hermes to find the old women of the gray lands and pressure them in to giving up the location of the Nymphs of the North to obtain the three magic gifts Winged Sandals, A Magic Wallet, and the Cap of Invisibility. With these gifts Perseus was ready to face Medusa.
The island where Medusa was imprisoned housed two other Gorgons which were invulnerable but 1 Medusa was able to be killed. When Perseus came to the island Athena spoke to him telling Perseus which Gorgon was Medusa so he could get in and get out fast.