Blood Simple is a neo noir film, the debut of Joel and Ethan Coen, writers and directors of Fargo, The Man Who Wasn't There, and Raising Arizona, among others. In the film, Julian Marty, a bar owner played by Dan Hedaya, hires a private detective, played by M. Emmett Walsh, to spy on his wife (played by Frances McDormand) to find out whom she is cheating on her husband with. The detective returns with photos showing that Abby is cheating on her husband with Ray (played by John Getz), an employee at the bar that Marty owns. Ray expects to have been fired, and when Marty doesn't fire him, he quits. Marty still owes a few weeks' wages, but threatens to shoot Ray if he comes back to the bar.

The film was lensed by Roger Deakins and originally released in 1984; it was re-released in 2001 in a "director's cut"; faux film historian "Mortimer Young" claims in an introduction to the rerelease that the Coens have removed some of "the boring bits" and added other parts. What the Coens actually did was to tighten the editing using the footage in the original film: shortening some shots and removing others altogether, as well as changing some of the music in the film. One example of changed music from the original VHS release is the removal of Neil Diamond's cover of The Monkees' "I'm a Believer" in favor of The Four Tops' "It's the Same Old Song."

The commentary on the DVD release is by "Kenneth Loring," the fictional artistic director of the equally fictional "Forever Young Films"; the director often has his facts scrambled. For instance, Loring claims that the scene with Ray and Abby driving in the rain talking about Marty was acted out in reverse as well as upside down, in order to synch the headlights passing the car just as certain lines were said. Loring claims that filming the scene backwards and upside down was the logical choice to get the timing right, and that the actors are wearing hair spray to keep their hair pointing "down." He does not explain why the rain on the windshield continues to run down on the final image, in defiance of gravity. Later in the commentary he claims that in scenes with both dialogue and music, the actors simply mouth the words and record them in post-production, so as not to interfere with the music; that Marty's dog is animatronic; that the sweat on various actors is "movie sweat," gathered from the flanks of Palomino horses; that Fred Astaire and Rosemary Clooney were at one time intended for the film; and that a fly buzzing about is not real, but the product of computer generated imagery. Towards the end of his commentary, Loring launches into a tirade against Merchant and Ivory Productions. Kenneth Loring was played by Jim Piddock, acting from a script by the Coen brothers.

The title was coined by Dashiell Hammett in his novel Red Harvest, where he used it to describe the addled, fearful mindset people are in after committing murder.

Warning: spoilers follow

Marty breaks into Ray's apartment, where Abby has spent the night, gets into a struggle with Abby and forces her outside, and is incapacitated by a knee to the groin; he leaves in his car as Ray comes outside buckling his pants. Ray hugs Abby, watching as Marty speeds down the street.

Marty becomes increasingly irritated with the couple's liasions and hires the detective to kill them, then goes on a fishing trip. The private detective goes to Ray's apartment and breaks in while the two are asleep; he steals Abby's revolver from her purse and goes outside. The gun has three bullets in it. The detective delivers a large manila envelope to Marty, telling him that the bodies are taken care of. The envelope contains a photo showing the two in bed together with several bullet holes apiece, leaking blood. Marty appears to be nauseated by the photo and excuses himself to the restroom with the photo. On the way back, he stops at his business safe, opens it, and removes $10,000 to pay the detective for the murders. He gives the detective the money and the manila envelope. The detective checks the money and shoots Marty--the only person who knew about hiring the detective for murder--and leaves Abby's revolver behind.

Ray arrives at the bar to insist that Marty pay him the wages he's owed--apparently the private detective has faked the photo he gave to Marty. Marty is sitting in a chair facing away from him; he doesn't respond to anything Ray says, and doesn't move when Ray steps on a gun, setting it off. Ray walks around the chair and sees that Marty is slumped forward, bleeding from the chest; he has a hole in his chest and a large pool of blood beneath the chair; blood is dripping down his hand onto the floor. Ray goes to retrieve Abby's gun from under a piece of furniture, and stands staring at it awhile: it is Abby's revolver. Ray is interrupted by Meurice, who arrives in the bar outside Marty's office. Ray runs to shut and lock the office door; Meurice calls for Marty, gets no response, and then tells a woman that it's ladies night--drinks are free--and puts The Four Tops' "Same Old Song," loudly, on the jukebox. Ray uses the noise from outside to mask his cleaning the office, and removes Marty's body, dropping Abby's gun into Marty's coat pocket.

Ray is driving down the highway when he hears a noise from behind: Marty is alive. He stops the car and jumps out, panicked, running over a field of dirt. On returning to the car, he sees that the back driver's side door is open and Marty is gone. He is crawling down the highway, muttering. Ray follows him with a shovel, intending to kill him, but is interrupted by an oncoming semi-tractor. He picks up Marty and drags him back to the car, forcing him in as the semi passes. Ray digs a hole and throws Marty in. He is in process of burying him when Marty discovers Abby's gun in his jacket pocket. He pulls it out, trembling, points it at Ray, and pulls the trigger. It clicks; he pulls it again, and again; Ray removes the gun from him and continues to bury Marty alive.

In the morning, Ray is standing outside his car in the field, smoking. The car seems uninclined to start. Finally it does, and he drives off.

Meanwhile, at his apartment the private detective burns the series of photos he used to fake a murder, and discovers that Mary has replaced the incriminating faked photo with a sign admonishing employees to wash their hands before returning to work.

At Abby's apartment, Ray tries to explain that he cleaned up Abby's mess. Abby does not understand what Ray is talking about, and they get into an argument. Ray thinks Abby is being coy for some reason he doesn't understand. The phone rings, interrupting their argument; Abby answers. The person doesn't say anything and Abby hangs up.

"Well, that was him."
"Who?"
"Marty."

Ray leaves. Meanwhile, Meurice checks his answering machine and gets a message from Marty claiming that a large amount of money has been stolen from the safe and either he or Ray took it. Meurice goes to confront Ray. Abby goes to Marty's bar to try to find out what Ray is talking about--Ray had returned with blood on his shirt and she had assumed that he and Marty got into a fight. Abby finds the bar ransacked, the safe's combination lock dented, chipped, and partially shattered. The private detective had been trying to break into the safe and was interrupted by Abby's arrival: he is hiding in the bar watching Abby move about. She picks up a towel from the top of the safe; a hammer falls out. Abby spins the dial but does not open the safe. The fish that Marty brought back from his trip are still on the desk where Marty was killed; they are now green with rot.

At her apartment, Abby lies in bed; she gets up to wash her face and hears someone enter the apartment. She calls Ray's name, then pushes open the bathroom door. Marty is sitting on the bed. He warns Abby "He'll kill you, too," then says "I love you," then pitches forward and vomits a torrent of blood. Abby wakes up. Ray is at his apartment packing. Abby thinks that Marty refused to pay Ray, that Ray broke into the bar to get his money, and that the two of them got into a fight and Marty was killed. Ray interrupts and tells her it was her gun at the bar, that he can't eat or sleep lately, and that Marty was alive when Ray buried him.

Abby leaves to tell Meurice that she thinks Marty is dead; Meurice leaves for the bar. Ray is at the bar; he opens the safe and finds the photo showing him and Abby in bed, bodies riddled with holes, blood staining the sheets. He leaves for Abby's apartment, and the private detective follows him. Abby arrives and turns on the lights; Ray is looking out a large window and tells Abby to turn off the light. Abby is reluctant to do so. The private detective is on top of a nearby building, watching the two through a sniper scope, and shoots Ray through the back. Abby runs to crouch beneath the window, takes off her shoes, and throws them at the light bulb, breaking it. The private detective arrives at Abby's apartment, and she goes to the bathroom to hide; outside the bathroom window is a precipitous drop. In Abby's sparsely furnished living room, the private detective bludgeons Ray with a large coin bank, then searches Ray's pockets for the forged photo. Failing to find it, he goes into the bathroom. Abby is not there; he looks outside the window, then reaches his arm over, finding a window to another room. He opens the window; Abby slams it on top of his wrist and drives a knife through his hand into the windowsill. The detective screams and shoots chiaroscuro holes through the wall, then punches through and removes the knife. Abby, dazed, backs out of the room and slides down the wall opposite the bathroom door, holding a gun. The door is partly closed; eventually the man's shadow darkens the doorway, and Abby fires through the door. The detective falls. "I'm not afraid of you, Marty," Abby says, and the detective laughs. "Well, ma'am, if I see him, I'll sure give him the message." The detective lies looking up at the underside of the bathroom sink. Water collects on its underside and drips down onto him.