Investigators are pitted against the Hermetic Order of the Silver Twilight,[1] which is attempting to raise the lost city of R'lyeh from the depths of the Pacific Ocean.

In addition to the work by the original authors, new material was supplied by Lynn Willis, and the book was illustrated by Andy Hopp, Charlie Krank, Badger McInnes, Mislet Michel, and Tom Sullivan.

"[5] In the June 1990 edition of Dragon (Issue 158), Jim Bambra called Shadows of Yog-Sothoth "good, but it is not as slickly written or plotted as [a later Chaosium publication] Masks of Nyarlathotep"; but he admitted that it contains "excellent scenes" where "horror elements are well presented."

He concluded, "Opportunities for role-playing, investigation, and combat abound with nameless horrors and the depraved cultists who worship the creatures of darkness.

Players who treated Cthulhu and his minions as simply big D&D monsters, chubby creatures ready to be harvested for their experience point value, were in for a rude awakening.