Two adventures that can be played as a mini campaign.

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."

... and The Temple of the Moon
"Adventure and intrigue in Peru. An investigator recieves a gold artifact through the mails from Peru, pitting him and his friends against a ring of international art thieves and perhaps against more sinister foes"

and a 12 page pull-out; the Theron Marks Society Field Manual, explaining various techniques used by this group of Cthulhu investigators.