The story of how British playwright A. A. Milne (Domhnall Gleeson) decided to write books instead. Moving his family to the country, he found inspiration for his series of books for children in his young son, Christopher Robin (Will Tilston) and his beloved stuffed bear.

As Milne's success grows and he becomes an internationally known author and his books become beloved by children around the world, the lives of Christopher Robin, his mother Daphne (Margot Robbie), and his nanny Olive (Kelly Macdonald) are changed.