The latest trailer for Season 4 of Boardwalk Empire highlights Jeffrey Wright's new character, Narcisse Valentin, who runs Harlem and is the latest rival to challenge Nucky Thompson (Steve Buscemi) and his Atlantic City empire. We also see footage of Michael Shannon's Nelsen Van Alden, Kelly Macdonald's Margaret Schroeder, Stephen Graham's Al Capone, and many more in the new season, debuting Sunday, September 8 on HBO with "New York Sour".