Flying home with Medusa's head, Perseus passes over Ethiopia and finds the princess Andromeda chained to a rock as a sacrifice to a sea monster sent to punish her mother's boast of surpassing the sea nymphs in beauty. Perseus either turns the monster to stone with the Gorgon's head or kills it outright depending on the version, then marries Andromeda after resolving a dispute with a rival suitor by showing him the head as well, petrifying him and his allies at the wedding feast.
Returning at last to confront the king who sent him on the errand and who has been mistreating his mother in his absence, Perseus reveals the head one final time, turning the king and his court to stone, before giving the head to Athena, who mounts it on her aegis, the goddess's shield or breastplate, where it continues to serve as a protective, monster-deflecting emblem. An old prophecy that Perseus would kill his own grandfather is fulfilled almost accidentally afterward, when a discus he throws at athletic games veers off course and strikes an elderly spectator who turns out to be the grandfather who had once tried to have him killed.
Andromeda's mother Cassiopeia, whose boast had provoked the sea monster in the first place, along with her husband King Cepheus and the sea monster itself, were later placed among the stars as constellations, a detail ancient astronomers used to anchor the whole episode to a specific, permanently visible part of the night sky.