It is 50 years since Casablanca opened up in America. Little did Humphrey Bogart know when he uttered the final line - This could be the beginning of a beautiful friendship - that he had just closed what would be one of the most enduring and popular movies ever. Aljean Harmetz believes that every movie is a creature built from accidents and blind choices - a mechanical monster constructed of camera angles, the chemistry between actors, too little money or too much and a thousand unintended moments. Her portrait of the making of an unmatched classic reveals some of the accidents: how the stars of the movie almost weren't Humphrey Bogart and Ingrid Bergman; how As Time Goes By nearly didn't make it to the final cut.