What story does the Marchesa share about the Cardinal in the nonfiction book, War in Val D'Orcia, 1943-1944?

In the entry for December of 1943, the Marchesa narrates the story of a Roman Catholic cardinal who, in an act of self-sacrifice, preserved the lives of a group of Jewish prisoners. His actions, for both the Marchesa and the reader, are a powerful evocation of the narrative's thematic focus on the transcendent value of human beings and of the need for self-sacrifice in support and recognition of that value.