In the midst of the 2008 financial crisis, a portfolio-manager named Jeremy Stancroft (John Heard) instructs his employees to neglect the best-interest of clients in order to increase company profits.
Meanwhile, Jim Baxford (Dominic Purcell), a former soldier and armored car driver, lives with his wife, Rosie (Erin Karpluk), in New York City. Rosie is in the process of recovering from a near-fatal brain tumor. Their health insurance has reached its limit, and Jim finds that he is unable to afford her continuing treatment. He decides to cash in the pension he earned from serving in the military, but learns that much of it is lost as a result of bad investments on the part of his financial adviser Sean (Edward Furlong). In addition, he finds himself in a $60,000 lawsuit as a result of bad real-estate investments conducted by his rogue financial adviser.
Jim frequently lunches with a colleague in the armored car business, and two NYPD friends. He borrows $10,000 from the colleague to pay for an attorney named Mr. Patterson (Eric Roberts) to sue his financial adviser, and arranges a meeting with an assistant district attorney to discuss wrongdoings on the part of his financial advisers. However, Mr. Patterson claims that he is unable to do anything and the assistant district attorney is unwilling to meet with him. Jim becomes frustrated at the loss of his money and his inability to pay for his wife's treatment and their mortgage. Because of his financial situation, his employer reluctantly fires him, as the company is not willing to trust him with large sums of money.
Rosie feels guilty for the financial strain that her illness has put on Jim and, unable to cope, commits suicide. Jim blames Wall Street financiers for ruining his life. Seeking vengeance, he purchases various firearms and grenades from an arms dealer, and begins a one-man army shooting spree on the Wall Street bosses that lost his money and contributed to the death of his wife. One by one, he kills those that have wronged him. Meeting with his friends at lunch, Jim casually admits to them that he is the Wall Street murderer. The three laugh it off, convinced he's joking.
The climax of the film has Jim staging a one-man assault and infiltration of a high-rise office building to confront and kill Jeremy Stancroft, the same ruthless and greedy banker who is indirectly responsible for Jim's financial situation. Jim plants a bomb across the street to act as a diversion and then assaults the office itself, ruthlessly shooting innocent office employees and staff in his path.
Sitting at Jeremy's desk, Jim tells Jeremy why he is targeting him, of his corruption and asks why he should let Jeremy live. The heartless Jeremy defends his actions, saying that the famous rich people of history didn't get rich by honest work and that capitalism is a survival of the fittest society, where the "strong survive and the weak die off". Jim shows him a picture of his wife and tells Jeremy he's the reason his wife is dead. Shortly as SWAT begins to approach the office, Jim puts the gun on the table and counts to three. Jeremy grabs the gun when Jim gets to two, bragging about how he "won". Jim accuses him of cheating. Not caring, Jeremy pulls the trigger, only to realize that the gun is empty, for Jim cheated too. Just then, SWAT smashes the window and shoots Jeremy dead. Jim pretends to be an innocent wounded victim, having been shot in the arm by a security guard earlier, and is escorted away by SWAT, who is convinced Stancroft was the perpetrator.
A few minutes later, Jim stands in the lobby of the office building. He watches emergency personnel come and go, having just been treated for the gunshot wound to his arm. He is recognized there by one of his NYPD lunchmates, who had been called to the scene. Without a word, Jim is led out of the building by his friend to the street, to freedom. The film ends with Jim walking away, voicing over that he intends to continue his killing spree of white-collar businessmen elsewhere.