In 1933, after leaving Dogville, while traveling with her father (Willem Dafoe) and his gangsters to the south of USA, Grace Margaret Mulligan (Bryce Dallas Howard) sees a slave ready to be punished in a property called Manderlay. The slavery had been abolished seventy years ago, and Grace becomes revolted with the attitude of the owners of Manderlay, keeping slaves in their cotton fields and following predetermined despicable rules called "Mam's Law". Grace decides to stay with some gangsters in Manderlay and give notions of democracy to the slaves and to the white family. When harvest time comes, Grace sees the social and economical reality of Manderlay.