Yes, this is fiction, an artistic interpretation of organized crime in LA in the 40's. If you don't need historical accuracy in your mob story, this show has great visuals, standout acting (notably Simon Pegg as an American loser comic, though he's just a guest star, and Robert Knepper as killer Sid Rothman) and fantastic music by Mark Isham. But the real star is the dialogue. Sure, the storyline is about as contrived as a Hollywood subway, but the scripts are perfectly hard-boiled and it's a gas just watching the characters dance around each other with candy in one hand and a gun in the other. Jon Bernthal's Joe Teague is the perfect antihero cop straddling the line, a palooka with an agenda, and I'll keep watching just to find out what that is. I just wish the shooting victims didn't all do the slow-motion spazz-out.
edit: So, this was meant to be a review of the show in general, after watching 3 episodes, not just this preview episode.