Anno Domini 1327, last week of November, in a rich Benedictine abbey on the slopes of the Apennines. Brother William of Baskerville, a learned Franciscan from England, comes as a special ambassador of the emperor on a delicate mission: he is to organize a highly political meeting between Minorites suspected of heresy and emissaries of the Pope. But soon his stay in the abbey proves to be an apocalyptic time of horror. William and his assistant Adson witness the most miraculous events and deaths, which are highly strange for an abbey. William is gripped by the fever of the investigation: far more than the dispute between the emperor and the pope, he is interested in the unmasking of the murderer and in the process he delves deeper and deeper into the secrets of the abbey. And he has to hurry: his worst adversary Bernardo Gui, a merciless witch and heretic hunter, believes that the devil is at work behind the incidents and has quickly found his scapegoats...