New Orleans is a city of many faces. The gaiety of Mardi Gras is juxtaposed with the rampant corruption that earned it the nickname "The City That Care Forgot." The genteel decline of the French Quarter, the location of the city's original settlement, stands in contrast to the rich opulence of the Garden District, where the Americans later built their mansions. Voodoo and Catholicism exist side by side. Behind it's shining mask the leering visage of the Mythos can be found.
I highly recommend this if you plan on running CoC game (or, to be honest, any other supernatural/mystery RPC) in 1920s NOLA. For a slim book (less than 100 pages) it pretty much covers all the bases.
What? It's a short-ish book (compared to some other books in the "Secrets of..." line) covering, well, New Orleans in the 1920s. So we get a history of NOLA, a tour of the French quarter, of the city, of the bayou area, a primer on Voodoo, and an adventure.
Yeah, so? This book was originally published in 1997 (as The New Orleans Guidebook), I think, then updated in 2007 (as Secrets of New Orleans); now, my usual cavil against books like this from that time is that I have the internet now, so you don't need to tell me a straight history of New Orleans.
This book ably sidesteps that cavil by giving me what I always claim I want: a view of the subject matter through the lens of the game. And! It's fine. There's enough relatively normal stuff to give a grounding for the elements of horror that pop up here and there throughout the book.
This volume is a fascinating overview of old New Orleans with a mix of historical information and Mythos-related fiction pertaining to larger-than-life Louisiana figures like Marie Laveau and Jean Lafitte. Some of the information pertaining to structures and facilities is out-of-date [the Louisiana State Museum is now in Baton Rouge], but some of these anachronisms are deliberate because the setting is 1920s New Orleans not present-day New Orleans. Nevertheless, the book is a wealth of information on voodoo and its relationship to the Cthulhu Mythos.