An elderly heiress is killed by her husband who wants control of her fortunes. What ensues is an all-out murder spree as relatives and friends attempt to reduce the inheritance playing field, complicated by some teenagers who decide to camp out in a dilapidated building on the estate.

Ferdinando Cefalù is desperate to marry his cousin, Angela, but he is married to Rosalia and divorce is illegal in Italy. To get around the law, he tries to trick his wife into having an affair so he can catch her and murder her, as he knows he would be given a light sentence for killing an adulterous woman. He persuades a painter to lure his wife into an affair, but Rosalia proves to be more faithful than he expected.

14th-century Franciscan monk William of Baskerville and his young novice arrive at a conference to find that several monks have been murdered under mysterious circumstances. To solve the crimes, William must rise up against the Church's authority and fight the shadowy conspiracy of monastery monks using only his intelligence; which is considerable.