For many years, a lone castle has stood on the edge of demonic lands, a beacon of light holding back a sea of darkness. But now it has fallen to the fiends who threaten to spread beyond to the civilized world. The Demon Within is a dungeon adventure for mid-level characters, compatible with the world's most popular fantasy roleplaying game, and part of the GameMastery Module line. GameMastery Modules also include four pre-made characters so players can jump right into the action and full-color maps and handouts to enhance play.