On a winter night, the priest of Saint Margaret, Don Guglielmo, has been found dead, apparently of natural causes. For a long time he was studying and keeping very jealously, three ancient parchments. Those text describe the existence of a mysterious treasure linked with an ancient esoteric cult: the Benandanti, or "Good walkers", and they seem to be connected with his death. His young niece and only heir, Arianna, unaware her uncle's studies, seems to not know about her uncle's conspicuous Swiss bank account. The controversial contribution of the eccentric professor Moretti, expert of popular traditions and ancient cults, in solving the case, doesn't lead to the desired solution. The case gets more intrigued when also the sacristan of Saint Margaret is found dead in mysterious circumstances.