The Minotaur demands human sacrifices, and every nine years, King Minos sends seven young men and women into the Labyrinth to meet their doom. One of these victims sent to his death is the hero Theseus. This guy is tough and he decides to fight back and try to kill the Minotaur. King Minos' daughter, Ariadne, falls madly in love with Theseus.
And since Daedalus built the Labyrinth, she asks him to help Theseus safely navigate it. Always the helpful one, Daedalus gives Theseus a ball of yarn, and tells the hero to trail it behind him, creating a roadmap for how to get back out.