Gangbusters: Weird Tales & Paranormal Investigations: The Blue Book Detective Agency Beginner Game (or Rules) is a revival of the 1980s Prohibition Era RPG. The biggest thematic change is the addition of magic.

From the 1st page:

WELCOME TO THE BLUE BOOK DETECTIVE AGENCY!

Interested in the Prohibition Era of the Roaring Twenties and Dirty Thirties? You are not alone! This is the roleplaying game of Gangsters, Gun molls [sic], Gumshoes, and G-Men.

The Blue Book Detective Agency Beginner Game is a preview version of the Gangbusters 1920s Roleplaying Game that provides players with a chance to try out the game system without much in the way of risk or obligation. The booklet you now hold gives you all the information you will need to create a Private Eye for the Gangbusters Roleplaying Game, as well as a brief overview of how to play the game and for one player as the Judge or referee, to run the game for the others. Many rules contained in the complete Gangbusters Rulebook have been omitted from The Blue Book Detective Agency Beginner Game so as to present a streamlined and simpler game.