In October 1867, the papal Rome, led by Pope Pius IX, is shaken by a bomb attack carried out in the sewers of the barracks of Palazzo Serristori, Rome, which kills twenty-three French pro-papal Zouaves. A countess, mother of secret revolutionary Cesare Costa, accused with friends Giuseppe Monti and Gaetano Tognetti to have organised this massacre, goes to a judge of the Holy See, Bishop of Priverno Colombo, asking him to help her.