"Grand catastrophes offer grand opportunities for grand men," a character comments about 50 pages into this novel about the first 27 days after Pearl Harbor.
That, in itself, is the theme of the book. That if you grab the moment there is a ton of money to be made and power to be had when something goes really wrong and people are terrified.
Perfidia is a grand and strange book in that it is a prequel (containing at least one character from each of Elloy's previous novels) but also a stand alone. You don't need to know that a given person will end up killing Martin Luther King in order to appreciate what's happening in the "now" of 1941.
The basic point going on is that not everyone thought it was a great idea to become part of World War 2. In fact, a bunch of people didn't really like Jewish people and really hated communists, so the idea of going to war with communists on our side just to protect Jews seemed like an asshole move.
So, these people looked to find ways to avoid a war against people they had no beef with. Most of these people are cops - and there is a draft rider that says that if a given cop is listed as "essential" then he or she is draft exempt.
This works wonderfully for the cops who like Hitler and don't want to fight him. They have enough clout to make sure they don't have to go off to war. In the meantime, because half the LAPD is going off to enlist they have a once in a lifetime chance to really change the world - i.e. there are a ton of job openings. They are moving up in the command - filling spots for people who are going off to the war. They can hire dumb goons to fill the empty spots. The dumb goons will do whatever they tell them to do. The war will last at least a few years. By the time it's over the entire culture of the LAPD will be changed. In other words - they have a chance to create institutionalized racism in the LAPD - and their guess is that if they do it right it will last at least 50 years.
This is the setting for this novel. It contains characters from every single other novel Ellroy has ever written. We are seeing these people when they are young. But, unlike Star Wars prequels they remain interesting.
The glossary of the book lists 48 main characters. But, really, there are only a few that matter that much. Here they are:
Dudley Smith: Ex IRA member who had his mom, dad, sisters and brothers killed by protestants. He left Ireland and joined the LAPD because he thought it would give him a good chance to beat up/murder protestants. Along the way though he realized that was short sighted and that as a cop he could run a ton of criminal enterprises. Is described in this book and in four other books as "the smartest man who ever lived."
William H. Parker. A police captain who wants to one day be the chief of the LAPD. He wants to be a good guy, but loves underage women, strong booze and perfidia itself. He and Dudley are arch enemies and he will become as brutal as Dud when he needs to be.
Kay Lake: A woman who fled the Dust Bowl during the depression, got sold into White Slavery and eventually got out thanks to the help of a brutal cop. She is always on the ropes. Intellectually she is a communist. But, she has a fetish for brutal cops. She goes back and forth between these two worlds. Each world wants her to betray the other - which world will she realize she reallly is a part of? Which will she betray?
Hideo Ashida - A man who knows he could be killed at any moment. He's the best CSI guy the LAPD has ever had. That's good in that when the cops need to solve a tough case they know he can do it for them. It's bad in that he'll know when they are framing someone. Plus this takes place when nearly every "Jap" is being interned. He wants to help Dudley, Parker and anyone else who will let him keep his freedom.
Bette Davis: A popular actress who has the money that people need to get their various scams off the ground. Beautiful, tough, but has a weakness for rough trade willing to eat her out.
John F. Kennedy - A young man with a wealthy dad who decides to join the Navy after Pearl Harbor to make himself look good. Is easily manipulated because he wants as much pussy as possible.
Elizabeth Short - A young woman who comes to LA to meet familiy members and decides to stick around. A quick Google search would reveal why that's an awful idea for her.
Through POV chapters from most of these people you get a new way to look at America in 1941. While not quite as great as White Jazz, it is as good as L.A. Confidential.
To explain why would only be possible if I included spoilers and I suspect Ward J. Little would beat me to death if I did so.