"S21" is the name of a former concentration camp for political prisoners in Cambodia. Former victims and tormentors caught up in the atrocities committed by the Khmer Rouge are reunited, and relive the inhumanity and cruelty of their days here. Facts that are brought to light by evidence presented here, and the vividness of the exchanges between two former adversaries transcend the twenty-five years that have passed. This film silently pulsates with the emotion felt by Cambodian-born director Rithy Panh toward his homeland.