P.L. Travers spent decades resisting Walt Disney's plans for her most famous creation, and Victoria Coren Mitchell traces why, starting long before Mary Poppins existed. Travers lost both parents while she was young, reinvented herself under a pen name, and later adopted a baby as a single woman, choices that shaped the guarded, difficult woman who eventually sat across from Disney's studio negotiators. The film uses interviews with Emma Thompson, who played Travers on screen, and producer Cameron Mackintosh, who dealt with her directly on the stage musical, to piece together what she actually wanted for her books versus what Hollywood delivered. Travers disliked the cheeriness, the animation, the songs, and made her objections known during production, a conflict that only became public knowledge decades later. Coren Mitchell treats the author as the more interesting story than the film she resented, following a private, unhappy life that produced one of cinema's most beloved family movies almost against its creator's wishes.