In July 1941, a political prisoner escaped from Auschwitz. As a punishment, ten others were chosen by the Nazis to be killed in a starvation bunker. One of these men, Franciszek Gajowniczek, began lamenting what his death would mean for his wife and children. Upon hearing these cries, another prisoner, a Franciscan friar named Maksymilian Kolbe—who had run afoul of the Nazis after sheltering refugees, including hundreds of Jews, at his friary—volunteered to take Gajowniczek’s place and was sent to the starvation bunker in his stead. In the bunker, Kolbe became the leader of those awaiting death, whom he was...