 "The Sinister Secret of Saltmarsh" is the first installment in a series of three modules designed and developed in the United Kingdom, for beginning adventures with "AD&D" rules.The adventure was written by David J. Browne with Don Turnbull, and published in 1981 as a thirty-two page booklet with an outer folder.The publication contains large-scale maps, a full background story, and detailed encounter descriptions for the players and Dungeon Master (DM).