Robert McCall (Denzel Washington) gets up early to go to work at Home Mart. McCall has an OCD that makes him time everything he does, from getting ready for work to just washing the dishes. He is respected and well-liked amongst his co-workers who have no idea of his past. On this day, he has lunch with his friend and co-worker Ralphie (Johnny Skourtis) whom he is in the process of helping lose weight. He questions Ralphie about his lunch and is satisfied with his answers until Ralphie takes a bite out of his sandwich and McCall hears a crunch and finds out there are chips in the sandwich. McCall reminds Ralphie he's supposed to be dropping weight for his test to become a security guard. He also reminds him to always aim for progress, not perfection.Most nights, McCall can't sleep so he took to going to a local 24/7 diner where he reads books and drinks tea. He is currently reading "The Old Man and the Sea." A young prostitute (Chloë Grace Moretz), with whom it is implied Robert talks to every now and then, asks McCall if the man in the book has caught the fish. He says not yet. The girl finishes her pie and goes to hail a cab.At work, a couple of McCall's young coworkers ask him what he used to do before working with them. He jokes that he was a Pip with Gladys Knight, doing a little dance for them.He goes back to the diner that night and runs into the same girl. She notices he's reading a new book. Robert tells her how the other one ended. As they are talking, a limo pulls up across from the diner. She then gets a call from her pimp, Slavi (David Meunier). He tells her she has a client, which is the man in the limo. She tells her pimp she doesn't want to work with this client because she finds him disgusting but her pimp ignores her feelings and tells her to go to work. The car door opens to reveal an obese man waiting for the girl. Reluctantly, she goes outside and joins him.The next night, McCall finds the girl at the diner but she has a bruise on her face. He gives her a doughnut that he got from work. Nervous, looking for a quiet voice, she decides to break their usual protocol and sits with him at his table. She introduces herself as Teri, although her real name is Alina. She hands McCall a CD that she recorded of herself singing hoping to get his opinion later. She aptly deduces that Robert has been recently windowed and still feels lost without his wife. Robert confirms she guessed right and reveals that his reading habits are inspired by a reading challenge his wife couldn't finish. The two of them leave the diner talking and walking for a while. As they're about to part ways for the night, a car pulls up to them. It is Slavi and his driver Tevi (Alex Veadov). Slavi gets out and slaps Alina. McCall considers interfering but is called off by Alina. Robert notices Tevi has a gun in his hand. Slavi walks over to McCall and hands him a card for his business and suggests he picks another girl.McCall then goes through a few days and nights without seeing Alina and is obviously worried about her. One night, he learns from the diner's manager that Alina is in the ICU after being beaten badly. McCall goes there and sees Alina's face even more bruised and messed up. He also notices she is with another girl, Mandy (Haley Bennett) who's crying uncontrollably. Robert doesn't go into the room but observes from a distance, unseen by the girls. Mandy later walks by McCall, crying. She gets a cup of coffee but overflows the cup. McCall comforts her and asks about Alina, explaining he's a friend. Mandy reveals that Slavi hit Alina and she hit him back. Slavi got mad and made an example out of her. Mandy says that Slavi also threw battery acid in a girl's face once and keeps her around as a reminder not to cross him. He treats his girls like merchandise and nothing more.McCall ponders on the situation for a few days before finally deciding to act. Using the card Slavi gave him, McCall goes to a restaurant where Slavi and his men are hanging out. McCall enters the office suite above the restaurant with an envelope containing $9800 which he offers for Alina's freedom. The goons laugh at McCall and Slavi explains that he makes so much money off of Alina being so young that $9800 could only buy her one month of freedom. He then laughs at McCall's offer and suggests he should go home and jerk off 9800 times. Then, maybe, Alina wouldn't be worth so much and he could consider freeing her. McCall takes the money back and starts to walk out. He almost leaves but then decides to stay and locks the door. After carefully observing the men and whatever weapons they may be holding, he sets the timer on his watch and moves into action. One of the men aims his gun at McCall, but he grabs the man's arm and causes him to shoot Slavi in the throat. He then jabs a shot glass into that man's eye. He stabs the third man with his own knife, and then gets a corkscrew and repeatedly stabs Tevi until he sticks it under his chin and finishes him off. McCall goes to Slavi's side and explains to him what his body is going through and that he'll be dead in a few seconds. Slavi asks "Who are you?," to which McCall doesn't answer and counts down the remaining seconds before Slavi loses consciousness and dies. Robert apologizes and goes home where he cleans himself up and actually sleeps all night for once.Following the murders, a Russian mobster named Teddy (Marton Csokas) arrives in Boston to investigate what happened to Slavi and his men. He teams up with a group of corrupt cops to gain leads. So far, everything points to a gang hit from a rival mob.At work, McCall notices Ralphie isn't in. He's told by a manager that Ralphie called in quits. McCall visits a restaurant that Ralphie's mother (Luz Mery Sanchez (as Luz Sanchez)) owns. Ralphie is helping her after a fire broke out, supposedly by accident.Meanwhile, Teddy is taken by one of the crooked cops, Frank Masters (David Harbour), to the workplace of a gangster named John Looney (Shawn Fitzgibbon), to continue his search for the killer. John insults Teddy, and all Russians in general. In response, Teddy hits John with an ashtray while Frank kills John's goons. Teddy continues to beat John's face in until the man goes unconscious.The other two dirty cops, Remar (Mike O'Dea (as Mike P. O'Dea)) and Pederson (James Wilcox), are eating at Ralphie's mother's restaurant. They extort her for protection money and claim that there will be another "accident" if the money isn't on time again next week. McCall finds them outside the restaurant and says he'd like to report a crime. They brush him off and tell him to call 911 until he calls one of them on his personal cell phone. McCall plays a video he took of them extorting a convenience store clerk during which they confess to starting the fire at the restaurant. McCall tells them they can either give the money back or the video will hit the news stations. The cops hold him at gunpoint, but McCall quickly beats them both. They comply and later return the money to Ralphie's mother.Soon after, McCall is seen playing baseball with his co-workers when Ralphie shows up in a security guard uniform, having passed his test.Back at work, Robert goes to see Jenny (Anastasia Mousis Sanidopoulos (as Anastasia Mousis)), a cashier, for a refund when he notices she's dealing with a man silently committing a robbery at gunpoint. McCall calmly comes over and gives him the money. The crook also demands Jenny's ring, which was her mother's. She tearfully hands it to him. McCall observes several details of the man, like his tattoos and his clothes. He considers making a move but doesn't since children are entering the store and could get harmed in the process. McCall instead follows the man outside and gets a good look at the car plates on his ride. The cops inform them that this was part of a string of robberies from the same man. McCall then goes to get a sledgehammer off a rack. The next day, Jenny finds her ring in the register and McCall is seen returning the sledgehammer to the rack after wiping it clean.Meanwhile, Teddy finds out about Alina missing from Slavi's girls and questions Mandy who says she didn't really know her that well. He later visits Mandy and intimidates her into revealing that she lied. He makes her talk about the night she visited Alina at the hospital and she talks about an unknown but kind black man who also came by and inquired about Alina although she never found out who he was. Teddy then strangles her to death for lying to him.With that new information in mind, Teddy finds video evidence of McCall going into the restaurant but none of him ever leaving. Pretending to be a detective, he visits McCall at his apartment who sees through him right away but still answers his questions with his prepared answers. Teddy leaves feeling McCall is a lot more than he lets on.Teddy obtains some more information about McCall, but what they can find about him shows a clean record with no trace that he has any involvement with Slavi's death. Teddy gets the feeling that everything they know about McCall is just made-up information. He and Frank, along with another villain, wait outside in a car while another guy enters the diner where McCall is eating. McCall makes up the man right away and asks him if they're waiting for anyone else. The man pulls out a gun and walks over to him. A truck pulls up in front of the diner, obscuring Teddy's view from his vehicle. McCall hits the man in the stomach with his book and then kills him by slamming his head down on the table and breaking his neck. He then kills the lights by sticking a knife in an outlet. He walks out of the diner and snaps photos of Teddy and his men in their car with his cell phone before walking away.Knowing where he lives, the gangsters follow McCall home. He boils some honey to tend to a wound sustained from the gunman while the gangsters silently enter his home. They burst into his apartment only to reveal that McCall is actually in another apartment, watching them with hidden cameras. McCall has planted evidence in his apartment that he is leaving town but Teddy doesn't buy it and feels that he is watching.McCall actually does leave town but only to visit his old friends Brian and Susan Plummer (Bill Pullman and Melissa Leo). They obviously have a history of working together for some intelligence agency. McCall asks Susan for information about Teddy and the people he works for. While she is out gathering information, Brian and McCall talk about McCall's car bomb accident that had everyone, including Brian and Susan, believe Robert was dead. Brian mentions that somehow, Susan knew Robert wasn't truly dead. When she returns, she tells McCall that the men he killed were part of the Russian mafia led by Vladimir Pushkin (Vladimir Kulich). Teddy, who is really named Nicolai, is the man Pushkin sends when something needs to be dealt with in no uncertain fashion. Remar and Pederson were on Pushkin's payroll but were found dead a few days earlier with their testicles shot off and shoved into their mouths. Susan warns McCall that these men won't stop until he and everyone he cares about is dead. Robert leaves the next morning after getting Susan's blessing to be the man he once was to finish what he started.McCall finds Frank Masters and traps him in his car, which he has rigged with a hose from the tailpipe. He tells Frank he better give him useful information about Pushkin's operations or he'll leave him in the car to die. Frank finally relents and takes McCall to a warehouse where the Russians count and stash huge pallets full of money, obviously millions of dollars in cash. McCall forcibly persuades the gangsters to surrender. He ties them up in a room with all the money for the cops to find. He then frees all the workers and gives them a departing bonus from Pushkin's money. He handcuffs Frank to a pole and tells him to call in a report. He then persuades Frank to be a good cop one last time and give him the information he knows Frank has probably stashed somewhere in case he ever needed leverage on Pushkin. When the police arrive, they find the gangsters, and the money, and arrest Frank. McCall goes to Frank's safety deposit box and retrieves some money, passports, and a USB stick containing more information detailing Pushkin's operations and revealing everyone currently on Pushkin's payroll, including cops, deputies, politicians, etc. McCall sends the information anonymously to the detective in charge of the warehouse bust. McCall also finds one of Pushkin's oil tankers and blows it up along with several trucks and a warehouse.Teddy calls in a team of assassins from Russia to help him track down and take out McCall. As he's having dinner with the team leader, the team leader goes to the bathroom. A few moments later, McCall sits in front of Teddy and drops the bloody sunglasses from the team leader letting Teddy know he won't come back. The two have a conversation in which Robert tells Teddy that he knows exactly who Teddy is and offers him a chance to stop everything before Robert finishes the job and takes out the entire organization. Teddy refuses the offer and arrogantly lets Robert know that he truly doesn't matter to him. Robert leaves the table after implying that he's not afraid to keep going. Teddy gets a call from Pushkin but he ignores it.Teddy finds a picture of Robert coming out of work with Ralphie and finally feels he has found a pressure point on McCall. Two of Teddy's men take Ralphie, Jenny and other Home Mart employees hostage, with the threat that they will kill them unless Frank meets Teddy where he blew up the tanker. The villains track his cell phone and await his arrival. When he doesn't show at the meeting place near the blown-up oil terminal, the henchmen in Home Mart prepare to execute one of McCall's coworkers. The music suddenly begins playing over the intercom. One of the mobsters takes Ralphie to find the source and is killed by McCall. The other hostage taker gets called away from the hostages by McCall speaking Russian and then gets also killed.Teddy and his other hired hands come to Home Mart. They try to find McCall and are steadily killed one by one as McCall stealthily moves about the darkened warehouse setting traps with tools found on location. He hangs one with barbed wire and stabs another one through the neck. He fights the biggest of the bad guys and is wounded until he finally kills him. Ralphie returns to help McCall and is shot in the leg. McCall lures one of the remaining bad guys to the break room. Ralphie turns the electricity back on as instructed, and the break room is destroyed when propane gas canisters in a microwave explode. Teddy is the last man looking for McCall when the propane explosion sets off the sprinklers. Teddy finds Ralphie and is about to shoot him when McCall comes out of hiding with a stud ram set gun and shoots Teddy with it several times until he walks up to him and shoots him in the throat, killing him. Teddy asks "Who are you?" to which McCall doesn't answer and watches him die. He then leaves the store.Three days later, McCall shows up in Pushkin's bathroom while he's showering in his Moscow home. McCall turns the lights on and off repeatedly and runs the sink water until it overflows. Pushkin talks to him for a few minutes and then McCall disappears. Pushkin retrieves his weapon from by the sink. He calls for his guards when he suddenly sees that McCall has cut the electrical wires and left them exposed on the floor. Pushkin is standing in the water when it reaches the wire and he is electrocuted and killed. As McCall leaves Pushkin's estate, he passes numerous guard bodies revealing he probably has killed everyone in the house.McCall returns to Boston to resume his quiet life now that everything is done. Bringing home groceries, he is approached by Alina, who is recovering from her injuries. She tells him she's gotten a real job and has started to do some reading. She also reveals she found an envelope with almost $10,000 inside with her stuff when she left the hospital. She thanks McCall for what he did, implying she somehow knows he's the one who got her free, and she kisses him on the cheek before they bid each other farewell.McCall resumes his quiet life only now he has found himself a new purpose. He has created an ad for people feeling trapped with all odds against them and no exit. One night at the diner, he receives a message asking for help. He simply replies, "Yes."