The story follows Harry Brown (Caine), a widowed Royal Marines veteran who had served in Northern Ireland during The Troubles, living on a London housing estate that is rapidly descending into youth crime.

Drew, commonly known by his stage name Plan B, recorded the film's theme music track "End Credits" with Chase & Status.

He lives on a London council estate ruled by drug dealers and violent youth gangs, while spending most of his time playing chess with his friend, Len Attwell, at a local pub owned by Sid Rourke.

When the hospital phones to tell him that his wife, Kath, is dying, Harry is too late to see her because he is scared to take a shortcut through a pedestrian underpass, which is gang-occupied.

Len confides to Harry that he is being terrorized by young hoodlums, and shows him an old bayonet he now carries to defend himself; with the police unable to help, he plans to confront his harassers himself.

The police arrest Noel Winters, the leader of a drug-dealing gang, along with members Carl, Dean, and Marky, but they are released due to lack of evidence.

Inside, Harry finds Kenny and his associate, Stretch, growing cannabis and sexually abusing an overdosing girl to make pornographic films.

At a press conference after the riot, Superintendent Childs announces that Frampton and Hicock are to be given awards (the latter posthumously), but stresses there is no evidence a vigilante was involved in the case.

The website's critical consensus states, "Its lurid violence may put off some viewers, but Harry Brown is a vigilante thriller that carries an emotional as well as a physical punch, thanks to a gripping performance from Michael Caine in the title role.

"[citation needed] Cinema Blend praised the film, saying "Caine pours every ounce of himself into Harry, and the payoff is massive ...