Background, suggestions, and guidance to help hosting Call of Cthulhu games. A wide listing of real-world occult books, and a detailed listing of Mythos tomes (with publishing histories, author profiles, variant editions, contents and new spells). A collection of arcane arifacts not covered by the rulebook. Descriptions of secret cults, alien races and places of mystery. A chapter on forensic medicine is handy when you want to add colour to crime scenes, or are facing questions from players who have been watching too much CSI. "Skills Revisited" is a chapter that gives suggestions on how to use skills under different circumstances, and expands on the skill descriptions in the rulesbook.

The optional rule of "brainstorming" is described, as is alternate rules on books and sanity loss.

Finally, in the back of the book there is a death certificat, ready to be copied, filled in, and handed out to your player when needed.