Filmmaker Joe Berlinger journeyed to Vienna, Austria, in 2002 to view the interment of the preserved brains of 700 disabled children executed at a so-called Nazi euthanasia facility. Among the perpetrators of the killings was Dr. Heinrich Gross, who conducted tests on the victims' gray matter. This elegiac documentary follows Berlinger as he attempts to learn why Gross was permitted to continue his vile experiments long after World War II ended.