In 1939, just finished the Spanish Civil War, Spanish republican photographer Francesc Boix escapes from Spain; but is captured by the Nazis in 1940 and imprisoned in the Mauthausen concentration camp, in Austria, a year later. There, he works as a prisoner in the SS Photographic Service, hiding, between 1943 and 1945, around 20,000 negatives that later will be presented as evidence during several trials conducted against Nazi war criminals after World War II.