This documentary addresses the tragedy that unfolded between 1975 and 1979 at the S-21 detention and torture center, located in the heart of Cambodia's capital, Phnom Penh. This former high school was transformed by Pol Pot and the Khmer Rouge into a site of extermination, where only three of the 17.000 prisoners survived. Twenty-seven years later, director Rithy Panh reunites two of these victims with several of their tormentors.