In his old age, Adso of Melk recalls a momentous week in November, 1327. With William of Baskerville he reached an abbey somewhere along the central ridge of the Apennines. William's mission was to mediate between delegations from Pope John XXII and Michael of Cesena, which would be meeting there. The purpose of this gathering was to ensure Michael's safe passage to and from the papal palace at Avignon, where he hoped to secure endorsement for various church reforms.
Upon arriving at the abbey, William received a second charge, as well: to solve the mysterious death of Adelmo, whose body had recently been discovered outside the monastery walls. The abbot, Abo, wants to know how and why Adelmo died, not only because he is concerned about the welfare of the monks but also because he does not want the papal delegation, led by the inquisitors Cardinal Bertrand del Pogetto and Bernard Gui, to use the suspected murder as an excuse for investigating the abbey.
Despite William's efforts, the mystery is still unsolved when the legations arrive. In fact, it has become even more puzzling. Two more monks have died: Venantius has been discovered with his head in a pail of pig's blood, and Berengar has drowned in a bath. Moreover, Severinus, the herbalist who has been aiding William, is killed on the morning of the meeting, and Malachi dies shortly afterward.
As the abbot feared, the papal inquisitors take advantage of these occurrences to learn that Abo has been harboring monks who once followed the