Domhnall Gleeson is hard at work brainstorming in the Goodbye Christopher Robin trailer, until his son makes a polite request: “I’d really like if you wrote a book for me. I’d definitely read it,” the boy says sweetly. As author A.A. Milne, Gleeson pens a book for his son, C.R. Milne, creating Winnie the Pooh, his friends, and the Hundred Acre Woods. The idea behind the whimsical plot helps the author cope with his post-traumatic stress following his return from World War I. Margot Robbie co-stars as Milne’s wife, Daphne, and Kelly Macdonald plays Christopher Robin’s nanny, Olive. When the books take off, the family deals with the price of international fame. Goodbye Christopher Robin will be released October 13.