From Carthidge to Mardor From the introduction: The realm of Opus is an organic, ever expanding campaign setting for the d20/OGL system which employs the retroactive method of developing a fantasy world through adventures instead of long-winded sourcebooks or gazeteers. Each adventure module in the Opus Operandi series provides the GM with all the information he needs on the location in which the adventure is set, and an overview of the campaign setting as a whole, both complete with maps. User summary: This sourcebook presents information about the setting originally presented in these five adventure modules: Opus Operandi: Escape From Carthidge Opus Operandi: Chains in the Dark Opus Operandi: Dark Side of the Sun Opus Operandi: A Pool of Clear Water Opus Operandi: Tower Down