Casey Sherman says the stage has become the next best place to get his stories exposed to audiences before taking them to the silver screen. His biggest success has been the story of the arrest of mobster Whitey Bulger, which he says has been a great tool to get Cape Cod actors on the stage as well. Next on his to-do list for a stage adaption: “Helltown,” the story of 1960s Provincetown murderer Tony Costa. The story is set to become a film starring Oscar Isaac and film on-location.