Aarow Jastrow is a Jew of Polish descent who immigrated to America with his parents and brother as a child. A close cousin, Berel, stayed behind in Poland. As a young man Aaron converted to Catholicism, which made him a black sheep to his family; all except his niece, Natalie, who never knew of his conversion. Aaron grew up to be a prominent intellectual and academic, eventually becoming a history professor at Yale University. He also became an internationally known author for his book A Jew's Jesus, which revealed the ancient Rabbinical tradition behind Jesus's teachings.
After retiring from Yale, Aaron moves to Siena, Italy, where he continues research for historical volumes. Natalie, who shares his passion for European history, moves there to be closer to him and to do his research.
The Jastrows' lives are changed when an old associate from Columbia University recommends that he take on a young man named Byron Henry as an additional research assistant. Byron is the youngest son, and himself a black sheep, from an American Naval family. His father, Victor "Pug" Henry, is a Naval Academy graduate and career Naval officer. His older brother, Warren, appears poised to follow suit. Byron, though he has successfulyl completed an NROTC course, has no interest in serving his country, and is instead drifting through life.
Though Natalie has had an on-again/off-again relationship with a diplomat named Leslie Slote, she soon becomes smitten with Byron. She enlists him to accompany her on an imulsive trip to Warsaw for the wedding of Berel's son. They end up arriving on the same dame the German Army invades. Byron proves himself useful in helping the extended Jastrow clan. Leslie shows far less bravery, and Natalie falls in love with Byron and agrees to marry him.
Despite warnings of the risks posed by staying in Axis territory, Aaron refuses to believe that anything the Nazis have planned for the Jews could possibly be worse than anything the Jews have suffered historically, and therefore refuses to leave. Natalie returns to Europe after her wedding to try to persuade him to leave.