Leonard Ketmeier is a medieval history professor theaching at Turin university, as well as an expert on satanism. One day he receives a letter requiring his presence at the S. Michele abbey. When Leonard talks to the abbot, he is told that a monk has been found beheaded in his cell and that strange signs have been drawed with blood on the wall close to the corpse. This is the start of an adventure that will bring Leonard to go into an investigation becoming more and more dangerous and worrying as necessary and urgent.