In 2009, Duch, former Khmer Rouge leader of the S21 prison, is accused of killing 14,000 people and judged by Extraordinary Chambers in the Courts of Cambodia (ECCC). Lawyer François Roux, who usually works with non-violent activists, and his Cambodian colleague Kar Savuth agree to represent him. The documentary tells the adventure of this Gandhi disciple working with a Pol Pot disciple, and the confrontation that results from their conflicting ideologies.