Oedipus the King Research Topic?

I have to write a research paper on Oedipus the King, but I am having a hard time coming up with a topic that I can properly research, document, and integrate with samples of the play. How could you research the idea of free will vs fate and tie it in? I was thinking of writing on the Oedipal Complex itself, but I am not sure how to narrow it down. Any ideas on topics that would fit a research paper needing sources would be greatly appreciated.