This is a great article posted on another site (who reposted it from another site, who took it from another), but I thought many would enjoy it here. It is The Lazy Man’s Guide for Constructing a Call of the Cthulhu Adventure, written by Sandy Petersen, original author of the Call of Cthulhu.
The ancient prophet Oijas Bek uttered a cryptic prediction:
In the time of the Floating Ships,
In the Capitol of the Shattered Empire,
The False God will draw the people to his banner,
The Blasphemer shall don robes of righteousness.
No one is sure what he meant, but the various sects each have their theories, which they often fight over.