In October 1942, SS guards at the Sachsenhausen concentration camp violently disbanded a rehearsal of a secret Jewish choir led by conductor Rosebery d'Arguto. Many in the group did not live to see morning, and those who survived were deported to Auschwitz-Birkenau. Only one of its members survived the Holocaust. Yet their story survives, thanks to Aleksander Kulisiewicz. An amateur musician, he was not Jewish, but became friends with d'Arguto in...