If you watch the film noirs of the 1940s, you can see they implied some pretty seedy subject matter. The Hays Code was in full effect, and so much we take for granted today was not permitted, but filmmakers were able to sneak things in around the edges. My favorite example occurs in Murder, My Sweet in which Phillip Marlowe is drugged, wakes up in a locked room after who knows how many days, and finds the criminals took his pants off but left his shoes on.
By the seventies and eighties, the so-called neo-noirs, or modern-day film noirs, could bring those repressed tendencies to the forefront. Consider the incest in Chinatown, the overt sexuality of Basic Instinct, and the squeam-inducing violence of Blood Simple. Angel Heart (1987), directed by Alan Parker, is one of the more graphic film noirs to come out of Hollywood with exquisite bloodletting, hallucinatory imagery, and Satanic subject matter.
In 1955, NYC private detective Harry Angel (Mickey Rourke) is approached by the mysterious Louis Cyphre (Robert De Niro) to track down Johnny Favorite, a famous crooner who disappeared shortly after the war before Cyphre could collect what was owed to him. Angel's investigation takes him to New Orleans where he gets involved with Epiphany Proudfoot (Lisa Bonet), a girl whose mother was involved with Favorite; a local Voodoo cult; and others. As Angel gets closer to solving the mystery, all the witnesses he talks to wind up brutally murdered, and Angel suspects Favorite is trying to cover his tracks.
Heavy on style, Angel Heart drips with atmosphere. The shadows, fans, steam, sweat, smoke, blood, it's palpable. Most of the classic film noirs take place in the night time streets of New York, Los Angeles, or similar urban places. While some of Angel Heart takes place in New York, most of its shot in wintry daytime, a stark contrast to the steamy New Orleans locations. It makes you glad for air conditioning. Other elements are more ominous: the blood-stained walls of the church where Angel first meets Cypher (the result of a suicide we're told), the chicken foot left for a guitarist who talks too much, and the demonic Hand of Glory owned by a fortune teller.
Essentially, Angel Heart is a story of doom, specifically Angel's. As he investigates, he encounters more death, more hedonism, and more information that was probably best left undiscovered. The classic film noirs existed in a world on a brink of destruction, whether it be by Nazis, Communists, or other forces. Traditional forces of good could only stand by helplessly ineffective or be in league with the evil. The difference in Angel Heart is the Satanic aspect; I highly doubt the Hays Code would have allowed it in its day. This angle could have potentially come off as hokey or over-the-top, but Parker, by cross-pollinating so many different genres, manages to keep it grounded.
I don't want to give away too much about the plot. There are a number of unexpected twists and turns along the way, and I'm sure you can guess one just by reading the plot summary. Rourke is solid, but it's De Niro who steals the show, casting a calm, detached amusement whose sinister undertones go without saying. Angel Heart is one of the better modern film noirs.