The powers of good are pitted against the forces of evil as the Duc de Richelieu wrestles with the charming but deadly Satanist, Mocata, for the soul of his friend. Mocata has the knowledge and the power to summon the forces of darkness and, as the Duc de Richelieu and his friends remain within the protected pentacle, they are subjected to ever-increasing horror until thundering hooves herald the arrival of the Angel of Death.