Short-tempered contract killer Raymond "Ray" Shoesmith is asked to help his best friend Gary after his wife Tatiana finds his urine-related pornography stash, so he pretends the tapes are his and lets Tatiana berate him. While out with his daughter Brittany, two youths intentionally knock into her and curse in front of her when Ray confronts them, so he has her wait in the car and beats them when out of sight. Walking back, he encounters Ally, a woman he met earlier while walking his dog, and the two exchange numbers.

Ray kidnaps and kills a man on orders from his handler Freddy, only to later learn he had the wrong person. Complying with the man's wishes for his family to know what happened to him, he anonymously informs the man's wife. Gary is beaten into a coma during an arms deal done alongside Vasilli, who Ray attacks after realizing his story is partially fabricated. After some interrogation, he learns that the deal was an orchestrated plot to rob Gary, and tracks down and brutally beats the men who hurt him.

Ray attends a court-ordered anger management therapy session following his beating of the youths who cursed in front of Brittany, where he is almost ejected after baiting another attendee into a fight. While recovering home alone from his injuries, Gary is robbed by Vasilli, but Ray saves him after Gary texts him for help. Gary shoots Vasilli in the forehead just as Tatiana comes home, and he distracts her while Ray starts to cut Vasilli's body up, only for him to wake up while getting his arm cut off. After Gary explains what Vasilli tried to do to him, Tatiana chases him out in a rage.

Meeting with Davros, Freddy's relative and a crime boss whose men Ray beat up after they beat Gary, Ray disrespects him. Despite Freddy's warnings to leave it alone, Davros sends three men after Ray regardless. Now dating Ally, Ray has a violent incident in a parking lot that she bears witness to, his outburst disturbing her. At a therapy session, Ray reveals his violent philosophy regarding people he views as detriments to society. That night, Ray notices Davros' men watching his house and lures them to a remote area, where he kills them with a Patchett submachine gun gifted to him by Gary. He returns home to Ally, who can smell the gunpowder on him but cannot identify it.

Ray and Gary discover that one of their associates is an undercover cop, but Ray decides to drive him out into the wilderness and let him go rather than kill him. He is later kidnapped by Dave and Bobby, two hitmen hired by Davros to collect and deliver Ray to him, but stalls for time by revealing he has a strongbox hidden holding more money than they are doing the job for. The hitmen privately plan to take the money and deliver him to Davros anyway, and Ray leads them to the strongbox but claims to not remember the combination. As Dave buys a gas cutting torch, Bobby leaves Ray in the trunk of their car to go buy cigarettes and both return to find the car gone.

Two petty criminals steal Dave and Bobby's car with Ray still in the trunk and sell it to a mechanic, who abandons it upon discovering Ray inside. Ray escapes from the trunk, later coming across the crooks with his strongbox and taking it back by force, only to be found and again kidnapped by Dave and Bobby. They drive him out into the woods to meet Davros, who demands the hitmen split Ray's money with them. As Bobby cuts it open, the empty, rigged strongbox explodes, giving Ray time to kill Bobby and Davros. He leaves Dave alive out of respect and buries the bodies, getting a call from Ally and claiming he will be late to meet her because of work obligations.

After Freddy hires two incompetent junkies that botch their corpse disposal, he sends Ray to kill them and get rid of all three of the bodies. Driving out into the wilderness, Ray finds himself connecting with one, but provokes the other into pointing a gun at him when he asks for him to put his ice pipe out. Ray intentionally crashes the car, killing both hitmen, and burns the remains.

Ray visits the mother of Brittany's classmate after learning she is being cyberbullied, but she remains adamant of her daughter's innocence and sends the police to his house after feeling she is being threatened. Understanding he cannot approach the girl himself, he sends Samantha to threaten her on his behalf. Later, he tells Ally how he was bullied as a boy and abused at home, and how he considered suicide but ultimately decided against it.

While out with Brittany and Ally at a carnival, Ray almost gets into a violent altercation, but Ally stops him. Brittany later walks in on Ally and Ray having sex, forcing them to awkwardly explain the concept to her. Ray's MND-stricken brother Bruce moves into his garage. Ray goes to collect debt from a man whose mother happens to be home, and he is forced to wait until she leaves, smashing a ukulele in the man's face for the inconvenience.

Ray is hired by an elderly man dying of cancer to find the body of his teenage daughter, having been missing for twenty-four years. Pointed in the direction of Dennis Miller, a convicted pedophile who was the prime suspect in her disappearance, Ray waterboards him until he admits he murdered her and stashed the body in a train tunnel. Ray has him lead him to the body and calls her father, allowing him to see it and take a locket from her body back. Miller feebly tries to apologize to the father as he leaves him alone with Ray, who stalks towards him.

Ray reluctantly promises Brittany he will give up smoking. At a Christmas party with Ally's family, he attacks her brother when he takes a gift meant for Brittany during a game of Secret Santa. When he tries to blame it on his inability to smoke and de-stress, Ally tells him that she left her similarly violent fiancée of three years after he started attacking her, and that she loves him but cannot risk it happening again, ultimately leaving him.

Ray collects Ally's things from his house and throws them out. He spends time with his dog in the park where he and Ally first met, but ends up getting into an argument with a woman who refuses to pick up her dog's excrement. He gets a job to strong-arm a woman blackmailing his hirer, only to negotiate a lower price when he learns the man had an extramarital affair that left the woman pregnant. He and Ally see each other at a supermarket and she leaves in a hurry, provoking him to drive to a park where she etched a heart into a tree for him and destroy it with an axe.

Ray takes Bruce to visit their estranged father Bill, refusing to see him and only coming in to help Bruce up and into the car. Hired by Alex, the vice president of a motorcycle club to kill president and old acquaintance Vinnie, Ray takes Gary out to Vinnie's family farm to act as a getaway driver. He dons camouflage and creeps towards the farm with a sniper rifle, but is caught on a security camera by Dave, now Vinnie's bodyguard, the camouflage concealing his identity. He takes shots at Vinnie and misses, fleeing with Gary. Later, he reads Jack and the Beanstalk to Brittany before bed, and adds on an ending where Jack is arrested for theft and murder after she expresses displeasure with him being the story's hero.

Freddy asks Ray to do him a favor and speak to a friend's daughter, a journalist writing a book on criminal mentality. He talks to her and reveals his complete indifference to the evil nature of his work. Ray and Gary kidnap Vinnie, who admits to Ray that he sees the people he has killed when he sleeps, and tells Ray that he will "see you in your dreams" before he is killed. Freddy fires Dirk, a bouncer and a military friend of Ray's, who robs him in retaliation. Freddy orders Ray to kill him, but he instead tries to convince him to leave town. Dirk states that he is haunted by his experiences in the military, including one where he killed a child, and instead chooses to commit suicide.

Dirk's daughter Maddy gets kidnapped while Ray and Brittany are out with her. Ray attacks a sex offender misidentified as the perpetrator and Davros' brother, who had threatened him earlier, both of them innocent. Meanwhile, Gary tracks down a man who had bought weed from a man who he discovered was a child trafficker, getting his location. Gary attacks him and his accomplices in their home, discovering Maddy being held in a secret room and locking them inside after taking her out. He returns her to her mother, while Ray goes to the traffickers' house and kills them with a shovel.

Freddy dissociates himself from Ray after the incident with Davros' brother. While out target shooting with his dog, Ray is attacked by two bikers sent by Alex and kills them, sustaining damage to his eye in the process. His dog is killed in the crossfire, and so Ray contacts Dave, who happily helps him kidnap Alex to pay him back for sparing him. Alex convinces them that he has a large sum of money hidden away and negotiates his life for it, and they drive off to go get it.

While they dig up Alex's money, he flees into the woods and escapes, despite the best efforts of Ray, Dave, and Gary, who Ray brought along as backup. They finish digging up the money and keep it. Ray and Brittany bury his dog. Bruce, now needing a wheelchair and not wanting to live with his disease any longer, indulges Brittany's obsession with being an actress by reenacting Romeo and Juliet with her. He and Ray drive to their run-down childhood home, where he begs his brother to forgive their father for his abuse. At Bruce's request, Ray euthanizes him with medication and burns the house down with his body inside.

Four men conspire to make an arms deal with Ray and Gary and rob them, having one of them pretend to be wounded to make it look authentic. Ray easily sees through this after the faker's friends steal the guns, making him call them and arrange a meeting to get the guns back. When he asks for the money they were going to pay him and is refused, he, Gary and Dave attack the men, killing them all except for the leader, who dies from his injuries after lamenting leading his friends to their deaths. Troubled, Ray chooses not to take a share of the money. Ray gets arrested and jailed after attacking a man over a traffic dispute, and befriends his cellmate Adam. Ray calls Brittany and asserts that everything is fine, not telling her where he is.

Freddy visits Ray in prison, hiring him to do a job for crime boss Rafael where he attacks a man with boiling water. Adam teaches him to meditate and they have a debate over whether or not violence is the proper way to settle conflicts, and Adam is eventually brutally attacked by an inmate he referred to as "champ", not knowing it to be prison slang for "cocksucker". Dave tracks down the man who got Ray imprisoned and threatens him into dropping the charges. Ray goes to see Brittany as soon as he gets out, who learned from a friend's mother that he was in prison. He tries to convince both her and the mother that the incident was not his fault, but he fails with both of them.

Gary, still hung up on his now ex-wife, spies on her and her new girlfriend but gets stuck on their balcony. He calls Ray to come help him, but Tatiana catches him descending the balcony, causing him to fall. Ray invites him to come live with him. He encounters a pregnant, married Ally while out, and the two have a peaceful, tender encounter before parting ways. The deteriorating Bill is detained after starting a fire in his apartment, and Ray reluctantly lets him move in, despite him believing Ray is Bruce. Later that night, Bill wanders off, and Ray is forced to track him down and bring him back home.

Brittany finds Ray's pistol and messes around with it, accidentally shooting a hole through her wall just as he comes home. She tries to hide it, but he notes her strange behavior and the smell of gunpowder and realizes what she has done, forcing him to tighten the gun's security. Gary asks Ray to go back to his old house and get something from his porn closet, and he has a hostile encounter with Tatiana and her girlfriend while there. The item turns out to be a sex toy shaped like a foot, which Ray does not understand the appeal of. Rafael hires Ray to do another job, disposing of an overdosed woman's body by feeding it to a drift of pigs, but he instead decides to bury it in the nearby woods.

Mistrustful of Brittany's new boyfriend Adrian, Ray has Gary come with him to a beach they are on and spy on them, only for Brittany to notice him. Gary starts a home pornography business, but only attracts the attention of a same-sex couple. The owner of Ray's frequented gym commits suicide after being scammed and losing his savings. Ray stops his son from hiring a hitman and offers to kill him for free, which he does by hanging him from his ceiling after taking all his money. Bill is moved into an assisted living facility, where he apologizes to Ray for his abusive childhood, lamenting how going to war changed him and wishing Ray could have known him as a better father before he changed.

Ray and Gary go to their high school reunion, where nobody seems to remember Ray. When Gary is continually made fun of by an old bully, Ray starts a brawl that gets them both thrown out. Adrian gives Brittany MDMA, and Ray attacks him, getting the location of the dealer and warning him never to talk to Brittany again. Ray catches the dealer receiving oral sex from an underaged girl, breaking in and waiting for her to leave before starting towards him, leaving his fate unknown. Ray and Brittany argue once she comes down from her high, but ultimately have a discussion where he admits he wants to shelter her from the evil he sees in the world, but acknowledges he cannot protect her forever and asks that she talk to him if she feels she needs to, which she agrees to.

Freddy's girlfriend approaches Ray for help when she notices him sporting various injuries, aware of his gambling addiction and debt. Ray approaches the crime boss Freddy owes money to and promises free use of his services in exchange for giving Freddy more time to repay his debt. Rafael has Ray accompany him on a drug deal, and he is forced to ride with Zoe, a university student. They find themselves getting along over the next couple of days, and, after a conversation about their past relationships, end up having sex.

Ray and Zoe take Polaroids of each other with her camera over breakfast. They hit a kangaroo while on the road and crash, and an elderly couple pulls over to help them after Ray calls Rafael, who arrives and kills them. Rafael promises to take the grievously injured Zoe to the hospital, while Ray drives the couple's RV out into the desert, buries their bodies, and spends the next day hiking back to civilization. He steals a car and drives it to the drop-off point, where Rafael informs him Zoe died en route to the hospital. Ray blames him for his handling of the situation and leaves, passing by the crashed car on the way, and stares at the sunset, deeply distressed.

Ray decides to sell his house. He takes Brittany to meet Bill for the first time, now seemingly at peace with him. As he sets up his trailer out in the wilderness, Gary informs him that his pornography business has taken off. Freddy sends Ray to go look for Alex, who has resurfaced, and he takes Dave with him, only to be ambushed by Rafael and two of his men. They shoot Dave, who dies of his injuries after begging Ray to take care of his young son. Ray kills Rafael's men, chases him down, and kills him. Realizing Freddy betrayed him, Ray confronts him in his home. Freddy insists Rafael would have killed him if he did not give Ray up, and Ray, to Freddy's surprise, leaves him untouched. Some time later, Ray has gained weight, grown his hair out, and started working as a taxi driver, keeping the picture he took of Zoe in his car's sun visor. He picks up two young men, who he realizes are planning to attack him. When one of them remarks that "someone might die out here tonight", Ray stops the car and grins knowingly at him, before looking at the viewer.