Black of Cowl, Blacker of Heart ... Consecrated by Christ himself, Glastonbury was the first Christian church in Britain. It survived the Roman persecutions, sheltered Arthur and Guinevere during the wars against the Saxons, and nurtured St. Dunstan, the greatest archbishop England has seen. Now a house of the black-robed Benedictine monks, it has fallen to diabolic corruption from within, and Satan is praised in God place. This is a dual-system d20 / Ars Magica supplement from the Coriolis line. It includes: Options for playing the adventure with either Ars Magica? rules or the d20 System? Diabolism rules for both systems, including the d20 System Diabolist prestige class, and information on Ars Magica demonic gifts, curses, and demonic servants. Details on the abbey of Glastonbury, its holdings, its diabolist inhabitants, and the powerful magical locations in the area. Story hooks to make Glastonbury a continuing feature of your campaign, even after the scenario portion of the book has been played through. Guidelines for running games in thirteenth-century Britain -- a setting that promises hours of medieval adventure!