Winner of the top prize in the Un Certain Regard category at the 2013 Cannes Film Festival, Rithy Panh's powerful documentary, employing archive footage and claymation, is an imaginative and unsettling journey back to the occupation of Cambodia by the Khmer Rouge in the 1970s. The film's premise lies in finding a picture, one that perhaps does not exist, to recall what happened during this period. The result is an extraordinary achievement.