Knowing that most film fans like to play 'What if,' film historian Harrison has taken over one hundred classic motion pictures and changed the casts and directors. Joel McCrea in 'Stagecoach,' Errol Flynn in 'Casablanca,' Cary Grant and Jean Arthur in 'Adam's Rib,' and Blake Edwards directing 'To Catch A Thief.' They're here with the original casts and 104 others. Harrison doesn't say the original filmmakers were wrong, as the motion pictures are indeed classics. But what if . . .