The Second Cthulhu Companion. Contains articles on various aspects of the game, including two 1920s scenarios: 'The Underground Menace' and 'Valley of the Four Shrines'.
From the back cover:
"Call of Cthulhu Questions Answered - Why does it take so long to read a Mythos tome? Why can't my investigator get 'used to' seeing common types of monsters? How do I learn a language in Call of Cthulhu? Must my character lose multiple Sanity for seeing multiple monsters?
The Ubiquity of Cthulhu - Working from the notes of brave Dr. Phileus P. Sadowsky (deceased), William Hamblin assembles ancient linguistic traces of the dread Cthulhu cult.
A Cthulhu Grimoire - Working summaries of all the spells from supplements Shadows of Yog-Sothoth, The Asylum, Cthulhu Companion, The Fungi from Yuggoth, Curse of the Chthonians, Trail of Tsathogghua, Masks of Nyarlathotep, and Fragments of Fear. Indispensible to keepers; deservedly horrifying to peeping players.
Scenario - The Underground Menace - Earthquakes hammer a hamlet in northern Michigan, but the townsfolk refuse to talk about the matter.
4-page Centrefold - Size-comparison silhouettes of selected Mythos deities, entities, monsters, species. See how big Great Cthulhu really is!
New Deities - Several new gods (and their servants) from the Mythos writings of Arkham House author J. Ramsey Campbell.
Scenario - The Hidden Valley - a dangerous quest leads the intrepid investigators into the 'heart of darkness' of the Belgian Congo jungles. This adventure may take several sessions to complete.
More - Model Ritual Curses, Innsmouth Street Map, a poem by H.P. Lovecraft, Mundane Animals from several continents, Sandy Petersen's introduction."