Science journalist Angela Saini and disability rights activist Adam Pearson, reveal that eugenics - the controversial idea that was a driving force behind the Nazi death camps - originated in the upper echelons of the British scientific community. The presenters uncover how shocking eugenic beliefs permeated the British establishment and intelligentsia; supporters included figures such as Winston Churchill and Marie Stopes. They see how eugenics influenced the Mental Deficiency Act of 1913, which resulted in thousands of disabled people being locked up for decades. Eugenics shaped immigration law, education policy and even town planning. The documentary uncovers disturbing links between British universities and German race scientists in the first half of the 20th century, and investigates how eugenics fed into the racist ideologies of Nazi Germany.