No wonder Mary Poppins needed a spoonful of sugar. The forthcoming Saving Mr. Banks is a dark film that tells the heart-breaking true story behind one of the great characters in children’s movie history. P.L. Travers (Emma Thompson), the nanny’s formidable creator, is pitted against Walt Disney (Tom Hanks), who promised his daughters that he’d bring Poppins to the big screen. The thing is, that pledge goes against the author’s wishes. Saving Mr. Banks goes behind the scenes of the ferocious battle to make what was to become the famous 1964 musical adaptation. For 20 years, Travers refused to grant...