My New Story

     I have been for the past few months working on a novel.  I know what I want it to be about but am having some trouble on how I want it written.  The premise of it is that a set of twins who were separated at birth.  One knows about the other but the other one doesn't.  They reason why they were separated was because if they come in contact with each other will bring about the end of the world.  One sister is trained to kill the other one.  It pretty much is one is told they are an angel to save humanity and the other is a demon to destroy the world.