If you want to write a screenplay...

Graham Greene, whose works include The Third Man and The fallen Idol, speaks in his memoirs of how for him "it is impossible to write a film play without first writing a story. A film depends on more than plot; it depends on a certain measure of characterization, on mood and atmosphere, and these seem impossible to capture for the first time in the full shorthand of a conventional treatment... The Third Man, therefore, had to start as a story rather than a treatment before I began working on what seemed the interminable transformations from one screenplay to another... The film in fact is better than the story because it is in this case the finished state of the story."