One of the Core game books for Cthulhu 5.5.

A sourcebook for the players in "Roaring Twenties" Cthulhu campaigns. This handbook contains a wide variety of information for the player. An overview of the Jazz age; historical and cultural facts about the era. How to become an investigator; occupations and skills for the cultist-basher. Information on research, communication, media, and equipment. If you are suffering under the delusion that guns will do any good against elder horrors, there is a chapter covering period firearms.