From the back cover:
Ghastly Adventures & Erudite Lore
The Cthulhu Companion is a collection of new Cthulhu mythos lore, scenarios, and rules additions to the game. From this volume the Investigators gain two new skills and a chance to encounter prehistoric monsters, find a missing uncle, stop cattle mutilations, and solve a kidnapping. The grim prisons of four continents plus new Cthulhu mythos deities, races, and monsters help the Keeper propel the Investigators to madness. Player-characters will reel from new phobias and insanity types.