From the front cover:
"Contains the complete Books of Mystery, Monsters, Demons, Sorcery, Shamans and Treasures. This fantasy role-playing supplement works with all systems."
Revised & Expanded edition includes "Treasures I/II"
The Books of Mystery sets up a new character class, the "Lords of Mystery." Monsters and Demons are what you would think, Sorcery and Shamans are spells and class differences from standard Magic Users. Treasure contains items from Earth lore and mythology; Treasures II has items from the science fiction future.