Knocking opens the door on Jehovah's Witnesses. They are moral conservatives who stay out of politics and the Culture War, but they won a record number of court cases expanding freedom for everyone. They refuse blood transfusions on religious grounds, but they embrace the science behind bloodless surgery. In Nazi Germany, they could fight for Hitler or go to the concentration camps. They chose the camps. Following two families who stand firm for their controversial and misunderstood Christian faith, KNOCKING reveals how one unlikely religion helped to shape history beyond the doorstep.