The Golden Dawn is a sourcebook for Call of Cthulhu, written by John Tynes, John T. Snyder, "Alan Smithee", Steve Hatherley, Garrie Hall, and Scott Aniolowski, and published by Pagan Publishing in 1996. It's based based on the PCs being members of the early Golden Dawn -- a famous occult secret society based in London of the 1890s. I began running a campaign using this in June 2006.
Material central to the campaign has been adapted from John Tynes' adventures "The Room Beyond" and "Sheela-na-gig" (from the sourcebook The Golden Dawn) along with Kevin A. Ross' "Signs Writ in Scarlet" and "Plant Y Daear", and Fred Behrendt's "Sacraments of Evil" (all in the adventure collection Sacraments of Evil).