In the late 1960s, the white South African government imprisons many black militant leaders, including Nelson Mandela (Dennis Haysbert), in a maximum-security prison in Cape Town. White guard James Gregory (Joseph Fiennes) is placed in charge of Mandela's ward because he can speak the Xhosa language and monitor the prisoners' communications. Over the course of Mandela's long imprisonment, his quiet leadership causes Gregory to rethink his previous racist views.