Robert McCall is a quiet man living a modest life in Boston, working at a home improvement store. To outsiders, he appears to be just an ordinary, helpful coworker, with a routine, mundane life. But Robert harbors a secret past, having been a black ops commando, a life he has promised to leave behind. He spends his nights in a local diner where he befriends a young prostitute named Teri, who is under the control of Russian gangsters. When Teri is brutally beaten by her pimp, Robert can no longer remain a bystander. He decides to tap into his old skills to protect Teri and confront her abusers. His desire for justice reawakens the dormant warrior within him, and he becomes a vigilante, setting out to equalize the odds for those who cannot defend themselves.

As Robert dispenses his brand of justice, he inadvertently ruffles the feathers of a powerful Russian crime syndicate. Their response is swift and brutal, sending an enforcer to deal with the disruption Robert has caused. What ensues is a game of cat and mouse, as Robert's actions against the gang escalate. Using his intelligence, combat skills, and strategic planning, Robert embarks on a dangerous path to dismantle the criminal network. His crusade against corruption and malfeasance leads to intense confrontations, exposing hidden enemies and old allies, and threatens to reveal the dark secrets of his own mysterious past.