The kings sends his daughter and grandson in a chest into the sea.
I know what you can get your mother. Medusa's head.
A fisher finds the chest and is confused but then opens it and saves the women and the baby.
Then Perseus grows up but the king of the island falls in love with Perseus' mother.
Polydectes tricks Perseus into getting Medusa's head as a wedding gift.
Then he goes to the gorgons cave and cuts off her head. And returns home. In journey he saves a princess who was chained about be sacrificed to a sea monster. When the monster arrives he turns it into stone saving the princess.
But when Perseus returns home he tells the king about tricking him into killing medusa and then, Perseus turns the king and his guest into stone.