Plot
Robert McCall, a former Marine and retired DIA/DCS officer, lives in Boston and works at a big-box home improvement store. He helps his colleague Ralphie train to become a security guard. Unable to sleep, McCall often spends late nights reading at an all-night diner, where he befriends Teri, a teenage sex worker trafficked by the Russian mafia. One evening, Teri shares that her real name is Alina and that she dreams of becoming a singer. McCall and Alina take a stroll, but Alina's pimp Slavi abruptly arrives, hits her and forces her into a car. Slavi hands McCall a business card for their escort service before driving away.
A few nights later, a badly injured Alina is admitted to the ICU at a nearby hospital. Upon hearing the news, McCall learns from her friend Mandy that Slavi is responsible for her condition. Finding Slavi and his men at their restaurant, he is bluntly refused when he offers to buy Alina's freedom, so he swiftly kills them all. Unbeknownst to McCall, Slavi and his men are part of a much larger crime syndicate led by Russian oligarch Vladimir Pushkin. Teddy Rensen, Pushkin's enforcer, arrives in Boston to investigate the attack. Aided by Boston police detectives on Pushkin's payroll, Teddy canvasses rival gangs in the area, beating Irish mob lieutenant "Little John" Looney almost to death to send a message.
McCall continues exacting vigilante justice on the criminals he encounters. He blackmails two corrupt cops into returning racketeering money to Ralphie's mother and beats a gunman with a hammer after he robbed the hardware store, taking a coworker's heirloom ring from her. Teddy kills Mandy after learning that she has concealed information about McCall. He visits McCall at his apartment, where both try to intimidate each other. Teddy and his goons later try to kidnap McCall, who eludes them.
McCall's former DIA colleague, Susan Plummer, identifies Teddy as Nicolai Itchenko, formerly of USSR secret police, with Spetsnaz background. He has murdered two of the Boston police detectives who failed to kidnap McCall; a third, named Frank Masters had not been heard from for days. Susan also briefs McCall on Pushkin's operation. McCall tracks Masters down and threatens him into helping take down one of Pushkin's money laundering warehouses. Masters and Pushkin's men are taken into custody when the police arrive and find a note left by McCall to "follow the money." He confronts Nicolai again, threatening to commit more damage if he continues to pursue him.
McCall destroys two of Pushkin's oil tankers. Nicolai abducts McCall's coworkers at the hardware store to force him for a meeting. To Nicolai's surprise, McCall skips the meeting and kills the men to ensure the safety of the hostages they were guarding. Nicolai arrives with his men, but McCall stealthily kills them with improvised weapons collected throughout the hardware store and later kills Nicolai with a nail gun to save a cornered Ralphie.
Three days later, McCall finds Pushkin at his Moscow mansion, kills the guards and tricks him into electrocuting himself. Alina, following her recovery, runs into McCall and shares that she has started a new life with the money that was left at her hospital bed (although she does not know it was by him). Inspired to continue helping others, McCall responds to online ads requesting help, calling himself The Equalizer.
