Idea for Screenplay for my own Film

For coursework, I have to write a screenplay for a film of my own creation. In March 2011, I read Phillipa Gregory's The White Queen which is told through the perspective of Elizabeth Woodville, Edward IV's wife, and in it is the story of a water goddess called Melusine. I then decided to base my screenplay around her and the french legend. My film is therefore a fantasy and historical hybrid.