It is the year 1504, Cesare Borgia has fallen and Imola, his headquarters, is wracked by violence. Two families, as in many Italian stories, are facing each other: Sassatelli and Vaini (corresponding to the Guelfi and Ghibellini factions). 

The boss of Sassatelli is Giovanni, known as "Il Cagnaccio," meaning a bad or threatening dog but also a violent, treacherous,  cruel person.

Il Cagnaccio is feared by everybody, but he and his soldiers are not in town when, at the end of June, Guido Vaini decides to attack Palazzo Sassatelli. His intention is to take back the control of the city and avenge the assassination of one of his captains by Gentile Sassatelli, brother of Giovanni. 

The army of Vaini, reinforced by Ghibellini families, takes the heart of the city and the Palazzo Sassatelli (now Palazzo Monsignani)—until the sound of Il Cagnaccio's army approaches from the city of Forlì. The rout is on, a bloodbath that claims Ghibellini lives, and likely some innocent ones as well. It lasts a night and the next day, and the epicenter of the violence is Vicolo Alidosi—known from that time on called Vicolo Inferno.