Two 1920s scenarios and an Investigator's Handbook for Call of Cthulhu.
From the back cover:
"The Pits of Bendal-Dolum: The investigators travel to tiny British Honduras in search of a lost archaeological expedition, but find evil beyond their worst nightmares.
The Temple of the Moon: Adventure and intrigue in Peru. An investigator receives a gold artifact through the mail from Peru, pitting him and his friends against a ring of international art thieves and perhaps against more sinister foes.
The Field Manual of the Theron Marks Society: The Theron Marks Society is an underground group of organized Cthulhu investigators. This manual explains all the investigative techiniques and tricks they have learned. The Theron Marks Manual is designed to fit into any campaign."