P.L. Travers (Emma Thompson), the author of the “Mary Poppins” series, is broke and has to consider giving away the film rights to Walt Disney (Tom Hanks), who has pursued her for 20 years. She is a grumpy, difficult woman who flies to Los Angeles and tells Walt she needs to have full creative control or else she will not sign the agreement papers.
The Sherman Brothers (B.J. Novak and Jason Schwartzman) and the film’s screenwriter invite Pamela to sit in on their rehearsal process, but she wants to change just about everything, afraid that they will take a story that’s important to her and turn it into something silly.
Meanwhile, Pamela is remembering her childhood that inspired her books her father encouraged her to imagine and make believe but was also an alcoholic who died when she was 10. She warms up to the idea of the film but changes her mind when she learns that a sequence will feature cartoons (dancing penguins).
Walt flies to London, now realizing that the Mr. Banks character is based on her dad and he promises that his intention is to touch an audience and not to make money.
She finally gives up the rights and invites herself to the premiere years later, where she ends up loving the finished film.