Call of Cthulhu RPG: The Keeper's Companion
The Keeper's Companion is your source for information blasphemous, forbidden, and handy. This book contains information on game mastering (13 suggestions for keepers on improving your games), listings for more than 60 occult books, a small section on languages and scripts (human and non-human), and more than 20 artifacts.
There is also background and information on 8 cults (Golden Dawn, Brotherhood of the Beast, Yellow Sign, etc.), two chapters on alien races and mysterious places, a very detailed chapter on forensics and death investigations, and a section with skill expansions and new skills.
If you enjoy designing your own game scenarios, this book is a tremendously useful tool to have in you keeper's library. With the wealth of information covered in this one volume, there is enough to allow you to design plenty of scenarios that will keep any team of investigators busy for a very long time (or drive them stark raving mad, whichever comes first).
The Keeper's Companion is a 208 page soft cover perfect bound book with black and white illustrations.