A brutal murder, a nefarious plot, a coded letter. After five hundred years, the most notorious mystery of the Renaissance is finally solved.

The Italian Renaissance is remembered as much for intrigue as it is for art, with papal politics and infighting among Italy’s many city-states providing the grist for Machiavelli’s classic work on take-no-prisoners politics, The Prince. The attempted assassination of the Medici brothers in the Duomo in Florence in 1478 is one of the best-known examples of the machinations endemic to the age. While the assailants were the Medici’s rivals, the Pazzi family, questions have always lingered about who really orchestrated the attack, which has come to be known as the Pazzi Conspiracy.

More than five hundred years later, Marcello Simonetta, working in a private archive in Italy, stumbled upon a coded letter written by Federico da Montefeltro, the Duke of Urbino, to Pope Sixtus IV. Using a codebook written by his own ancestor to crack its secrets, Simonetta unearthed proof of an all-out power grab by the Pope for control of Florence. Montefeltro, long believed to be a close friend of Lorenzo de Medici, was in fact conspiring with the Pope to unseat the Medici and put the more malleable Pazzi in their place.

In The Montefeltro Conspiracy, Simonetta unravels this plot, showing not only how the plot came together but how its failure (only one of the Medici brothers, Giuliano, was killed; Lorenzo survived) changed the course of Italian and papal history for generations. In the course of his gripping narrative, we encounter the period’s most colorful characters, relive its tumultuous politics, and discover that two famous paintings, including one in the Sistine Chapel, contain the Medici’s astounding revenge.