Eamon Duffy. Saints and Sinners: A History of the Popes. 3rd ed. Yale, 2006.
Richard McBrien. The Lives of the Popes: The Pontiffs from St. Peter to Benedict XVI. HarperOne, 2006.
Jon M. Sweeney. The Pope Who Quit: A True Medieval Tale of Mystery, Death, and Salvation. Image Books, 2012.
John O'Malley. A History of the Popes: From Peter to the Present. Sheed & Ward, 2011.
Music: "Evening Melodrama" by Kevin MacLeod (www.incompetech.com)